Just looking at this dessert makes me happy. Everything about this cake, from the Willy Wonka-esque candy topping to the rainbow of multicolored cake layers, makes me happy. And to really gild the lily, the center of the cake is filled with sprinkles and even more candy, releasing an avalanche of joy when you cut into it.
Maybe you’ve seen cakes like this on Pinterest, your favorite baker’s Instagram feed, or even IRL at your best friend’s house and thought to yourself, “That cake looks so fun and complicated; I could never make that.” Otherwise, I’m here to encourage you! This stunning, show-stopping surprise-inside rainbow layer cake is completely doable from scratch.
True, it will take some time and preparation, but we have the step-by-step directions to create this beautiful (and delicious) cake at home.
Why You Should Make Rainbow Surprise Cake
This rainbow cake is the most outrageously joyful celebration dessert, ideal for a surprise birthday party. With a technique that’s easier than even the simplest surprise-inside cake, a rainbow layer cake filled with colorful candy will delight your birthday party guests of all ages. Fluffy vanilla cake makes up the colorful layers, while sweet, rich buttercream frosting make this surprise cake taste even better than it looks. It’s even more enjoyable than Funfetti.
This cake is going to take more time than your average birthday cake, but if you break the preparation up over two or three days, it makes the process smoother, less rushed, and easier to accomplish. Who goes first? The rainbow cake layers were colored and baked.
The Best Cake for Rainbow Cake Is White Vanilla Cake
Snow-white cake batter takes readily to a rainbow of hues — no fighting yellow cake’s buttery color. This fluffy white cake uses cake flour, which makes it less prone to overmixing (a legit concern when you must divide and color the batter six different ways).
Otherwise, there’s nothing different about the batter despite the coloring that will happen later. Using a paddle attachment on a stand mixer, beat together the butter and sugar, then add the egg yolks before alternating the dry ingredients with the milk. Since this is a huge volume of cake, you’ll want to stop and scrape down the sides of the mixing bowl on a frequent basis. The creamed butter and sugar sometimes hide in the bottom of the basin. Now that you’ve made your basic batter, it’s time to create those rainbow layers.
How to Make One Cake Batter and Color It 6 Ways
We now come to our first hurdle of baking this cake: You’ve got six layers to bake and only two cake pans (or you’ve got three or more cake pans, but not an oven large enough to accommodate them all), but that is more than fine! Cake batter is tougher than we give it credit for.
We’ll combine two layers at a time. When you pair the colors correctly, you won’t have to wash the bowl between every single batter.
Now, you are going to have to wait for the first two layers to bake and cool enough to remove the cake from the pans, clean your baking pans, and repeat dividing the batter, baking, and cooling, but the cakes only bake for 20 minutes and can be removed from the pan before they are completely cool. Chilling for 30 minutes will result in cakes that are firm enough to be removed without injury.
Here’s the order to follow and how to do it.
- Red batter then orange batter .
- Yellow batter then green batter .
- Blue batter then purple batter.
- To begin, spray two (9-inch) cake pans with cooking spray and line with parchment paper.
- Then weigh out 12 1/2 ounces of batter (this is roughly 2 cups) into a clean bowl. Add a teaspoon of red food coloring and mix gently to combine.
- Pour the red batter Scrape as much batter from the bowl as possible into one of the prepared cake pans.
- Now, measure out another 12 1/2 ounces of batter (almost 2 cups of batter) and add a teaspoon of orange food coloring . Bake these two cakes in the oven. Cover the mixing bowl of batter with plastic wrap and clean and dry the bowl you used for coloring.
Mistakes to Avoid When Building a Rainbow Cake
- Don’t rush: Make the cakes one day and put them together the next. Plan to refrigerate the cake for either a few hours or overnight before serving, so make space for it ahead of time.
- Don’t shortcut the cavity building: Use a circular cutter for removing the center from two cake layers, instead of building the cake and then cutting out a hole with a paring knife. This one move will give your cake a more polished, professional appearance.
- Don’t just throw candy in there: Line the cavity with frosting so that some of the sprinkles and candy will stick to the insides of the cavities. When the candy slips out, the aperture will seem fuller. For the longest-lasting candy filling, use coated candy and jimmy sprinkles. Chocolate and gummy candies sweat inside the cake.
- Don’t cut the cake right away: When the frosting has set, the cake will be sturdier, making it simpler to slice and serve.
The Best Frosting for Rainbow Cake Is Simple
Here is my philosophy — invest your baking time in making the beautiful rainbow layers and make a basic buttercream. You may use your favorite recipe, but you’ll need to double the proportions for the filling and topping.
How Do I Actually Build a Rainbow Surprise Cake?
You’ve got your cooked cake layers, buttercream frosting, and around two cups of sprinkles, coated candies, and edible glitter, and it’s time to put them all together. Don’t be alarmed! Stack the wrapped cakes to determine the sequence in which your layers will go. And finally split your six cakes into three sets of two: bottom layers, middle layers, and top layers. A hole will be cut in the centre of the two middle layer cakes.
Line a cake dish with parchment paper and set aside: In the middle of your cake plate, place a dollop of frosting. Line the cake plate with 4 strips of parchment paper to keep the cake plate clean while you frost.
Unwrap, stack, and frost the two bottom cakes: Remove the parchment paper from the purple cake layer. Put it in the middle of the cake dish. Smooth a uniform layer of 3/4 cup frosting over top. Some crumbs may stick into the frosting, but don’t worry — you won’t see them once the cake is complete. Remove the parchment paper circle and unwrap the blue cake layer. Invert the blue layer on top of the purple layer, making sure to align the two cakes as much as possible. About 3/4 cup frosting should be used to frost the top of the blue cake layer.
Unwrap the two middle layers, punch holes in them, and stack them: Remove the green cake layer but leave the parchment circle in place. Use a 3-inch-wide round cutter to cut a hole in the center of the green cake layer, then use an offset spatula to remove the small round of cake. Invert the green cake over the blue layer using the parchment paper from the green cake. Remove and dispose of the parchment paper. Coat the green ring with 1/2 cup icing, avoiding the hole for the time being. Rep unwrapping, punching a hole, and going to the yellow-layered stack of cakes. Take the parchment paper from the yellow cake and frost the yellow layer with 3/4 cup frosting. This time, apply a tiny coating of frosting to the inside of the cake’s hole.
Fill the cake with sprinkles! Fill the cavity with sprinkles and candy in the green and yellow layers. Press the sprinkles into the sides and bottom of the cavity, being sure the center is quite full and packing in the sprinkles as necessary.
Unwrap, stack, and frost the top two layers: Remove the parchment paper from the orange cake layer. Place the orange cake layer on top of the yellow cake layer and align the cakes as much as possible. 3/4 cup frosting should be used to frost the top. Unwrap the red cake layer, peel away the parchment paper, and level the cake if necessary. Invert the red layer on top of the orange layer, ensuring that the two cakes are as aligned as possible.
Crumb coat the cake: Spread half of the remaining frosting on top of the cake using an offset spatula to create a thin layer on the top and sides. Some crumbs will be picked by the frosting, but don’t worry — you’ll cover those with another thin layer of frosting in a bit. One hour before serving, place the crumb-coated cake in the refrigerator.
Frost and decorate the cake. Top the cold cake with the remaining frosting and again spread into a thin, even layer on the top and sides of the cake. When desired, top with extra sprinkles, candies, and toppings.
Cutting and Serving Your Rainbow Cake
Before slicing and serving, place the final cake in the refrigerator for at least one hour, if not overnight. To cut through the final cake, use a long, sharp knife, and be prepared for some resistance when the tip of the knife passes through the sprinkles. You’ll also need a spoon to scoop some of the sweet filling from the cake onto each dish.
For the biggest wow presentation, try to cut out one or two pieces away from direct view of your guests and then turn it around to reveal the cake layers. Some sprinkles and sugar may cling, so jiggle the cake a little to get the full effect!
Each layer is a different hue, and within this ultimate rainbow cake lies a delectable surprise. Here’s a step-by-step recipe to make it yourself!
For the cake layers:
- Cooking spray
- 4 1/2 cups cake flour
- 1 1/2 tablespoons baking powder
- 1 teaspoon fine salt
- 3 cups granulated sugar
- 3 sticks (1 1/2 cups) unsalted butter, at room temperature
- 8 large egg yolks
- 2 cups whole milk
- 1 tablespoon vanilla extract
- 6 teaspoons food coloring gel (6 colors, 1 teaspoon each, such as Cake Craft Coloring Gel Startup Kit)
For the American buttercream (makes about 6 cups):
- 1 pound (2 cups) unsalted butter, at room temperature
- 7 to 8 cups powdered sugar, divided
- 2 tablespoons heavy cream or milk
- 2 teaspoons vanilla extract
Day 1: Bake the cake layers
- Prepare your cake pans: Line 2 to 3 (9-inch) round cake pans with parchment paper rounds and coat with cooking spray. Preheat the oven to 350°F with a rack in the center.
- Combine the dry ingredients: In a large mixing basin, combine the cake flour, baking powder, and salt.
- Cream the butter and sugar: With a stand mixer equipped with a paddle attachment, beat the butter and sugar on medium speed until the mixture is lightened in color and slightly increased in volume, approximately 5 minutes.
- Add the egg yolks: Stop the mixer and scrape down the sides with a rubber spatula. Return the mixer to low speed and add the egg yolks one at a time, allowing each to fully incorporate into the batter before adding the next.
- Combine the milk and vanilla: Stop and scrape down the sides of the mixer. In a measuring cup, combine the milk and vanilla extract.
- Alternately incorporate the dry ingredients and the milk mixture: Combine 1/3 of the flour mixture in the mixer on low speed. Stop and scrape down the mixer. Add half of the milk mixture and mix on low speed. Stop the mixer and scrape it down. Add another 1/3 of the flour mixture to the mixer and combine on low speed. Incorporate the remaining milk mixture on low speed. Stop the mixer and scrape it down, then add the remaining flour mixture.
- Mix for 3 minutes on medium speed: Stop the mixer and scrape the whole bowl again. Go to the bottom of the mixing bowl, where butter and sugar like to lurk, causing your cakes to color and bake unevenly. Return the mixer to medium speed and beat for 5 minutes, or until the batter is fully smooth.
- Divide and color the batter: You’ll bake 2 or 3 cakes at a time, depending on the number of cake pans you have and the capacity of your oven. You’ll have about 4 pounds, 13 ounces of batter, so weigh out 12 1/2 ounces of batter (about 2 cups) into a small bowl. Mix in 1 teaspoon of gel food coloring using a rubber spatula. Fill a prepared cake pan halfway with the colored batter. Duplicate with another cake layer’s batter, a clean dish, and a different color of food coloring. If you have a third cake pan, make a third layer of cake batter. Cover the remaining cake batter with plastic wrap and set aside while baking the cakes; it’s best if you only portion the batter you need at a time.
- Bake the cakes: Bake the 2 to 3 colored cakes you’ve portioned and dyed for 15 to 20 minutes, or until the cake is firm, springs back when touched, and pulls away from the edges of the pan.
- Cool and wrap the cakes: Cool the cakes for approximately 30 minutes on a cooling rack. Remove the cakes from the pans, keep the parchment paper on, and immediately wrap each still slightly-warm cake separately in plastic wrap. Let to cool to room temperature.
- Divide the batter, color it, and bake it again: Wash and dry your cake pans and line again with parchment rounds and cooking spray, set aside. Repeat dividing the batter, coloring it, and baking until all of the batter is used up. The leftover cakes should be cooled and wrapped. Let it sit at room temperature for up to 1 day.
Day 2: Make the frosting and build the cake
- Beat the butter: In the bowl of a stand mixer equipped with a paddle attachment, cream the butter on medium speed until smooth.
- Gradually add in the sugar: Reduce the mixer speed to low and gradually add the 7 cups of sugar. Once it’s all added in, increase the speed to medium-low and mix until thoroughly combined.
- Add the liquid ingredients: Lower the mixer speed to low, then add the cream or milk and vanilla extract and beat until mixed.
- Whip until creamy: Mix everything together on medium speed until smooth and creamy.
- Add the remaining sugar: Reduce the mixer speed to low and add in the remaining 1/2 to 1 cup of sugar until the buttercream is as firm as you want it. Increase the mixer speed to medium and continue to beat until the mixture is frothy.
- Designate your cake layers: Arrange the still-wrapped cakes in the order you want your rainbow to appear. Choose which cakes will form the center two tiers. For our purposes, purple and blue will make the foundation of the cake, green and yellow the center, and orange and red the top two layers.
- Build the foundation of the cake: In the middle of a cake or serving dish, place a dollop of frosting. Line the cake plate with four strips of parchment paper to keep it clean while you ice it. Remove the parchment paper from the purple cake layer. If necessary, level the cake with a long, serrated knife. Level the cake and place it in the middle of the cake plate. Smooth a uniform layer of 3/4 cup frosting over top. Some crumbs may get stuck in the frosting, but don’t worry, they won’t be visible after the cake is finished. Remove the paper and level the cake after unwrapping the blue layer. Invert the blue layer on top of the purple layer, ensuring that the two cakes are as aligned as possible. Smooth a uniform layer of 3/4 cup frosting over top.
- Make the filled layers: Unwrap the green layer, leaving the parchment in place, and level if necessary. Cut a hole in the middle of the green cake layer with a 3-inch-wide round cutter and remove the little round of cake using an offset spatula. Use the parchment paper from the green cake to simply flip the green cake over the blue layer, aligning the cakes as much as possible. Take off the parchment paper. Coat the green ring with 1/2 cup frosting, avoiding the hole. Repeat unwrapping, leveling cutting a hole, and placing yellow cake on top of the green cake. Remove the paper and coat the cake with 3/4 cup frosting, including a thin layer of icing within the cake’s hole.
- Fill the cake with sprinkles: Fill the hollow with sprinkles in the green and yellow layers. Press the sprinkles in the sides and bottom of the cavity, being sure the center is quite full and packing in the sprinkles.
- Make the final layers: Remove the orange layer’s parchment and level if necessary. Align the orange layer with the other layers and place it on top of the yellow cake layer. Smooth a uniform layer of 3/4 cup frosting over top. Remove the orange layer’s parchment and level if necessary.
Invert the red layer over the orange layer and try to line the cakes as much as possible.
- Crumb coat the cake and chill: Place 1/2 of the remaining frosting on top of the cake and use an offset spatula to spread it into a thin layer on the top and sides of the cake. The icing will pick up some crumbs, but don’t worry, you’ll cover them with another thin coating of frosting shortly. 1 hour before serving, place the crumb-coated cake in the refrigerator. Set aside the remaining frosting at room temperature, wrapped in plastic wrap.
- Frost and decorate the cake: Top the chilled cake with the remaining frosting and spread into a thin, even layer on the top and sides of the cake. If desired, top with extra sprinkles.
- Cut and serve the cake: Refrigerate the cake for at least 1 hour more or even overnight before slicing and serving. To cut through the final cake, use a long, sharp knife, and be prepared for some resistance when the tip of the knife passes through the sprinkles.
- Make ahead: Bake the cake layers and set them aside at room temperature for up to one day.
- Storage: The assembled cake will keep in the fridge for up to 5 days.