How To Make the Ultimate Rainbow Surprise Cake

Just one look at this cake leaves me grinning. Everything from the Wonka-esque candy topping to the rainbow of colorful cake layers makes me giddy. 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.” I’m here to encourage you otherwise! You can totally make this knock-out, show-stopping surprise-inside rainbow layer cake from scratch.

Yes, it will take some time and some planning, but we’ve got the step-by-step instructions to make this great-looking (and great-tasting) cake at home.

This rainbow cake is the most fun, over-the-top celebration cake, perfect 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 is, dare I say, even more fun 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. Up first? Coloring and baking the rainbow cake layers.

Snow-white cake batter takes readily to a rainbow of hues — no fighting yellow cake’s buttery color. This fluffy white cake calls for cake flour, making it less susceptible 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. Butter and sugar are creamed together with a paddle attachment on a stand mixer, then egg yolks are added before the dry ingredients are alternated with the milk. You’ll want to stop and scrape down the sides of your mixing bowl regularly, as this is a large volume of cake and the creamed butter and sugar often hide in the bottom of the bowl. Now you’ve got your basic batter and it is time to make those rainbow layers.

Need a refresher? How To Make a Cake from Scratch

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 more resilient than we give it credit for.

We’re going to mix up 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. Cooling for 30 minutes will make for cakes that are study enough for removal without damage.

Here’s the order to follow and how to do it.

1. Red batter then orange batter.
2. Yellow batter then green batter.
3. Blue batter then purple batter.

1. First, coat two (9-inch) cake pans with cooking spray and a round of parchment paper.
2. 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.
3. Pour the red batter into one of the prepared cake pans, scraping as much batter from the bowl as possible.
4. Now, weigh out another 12 1/2 ounces of batter (again, close to 2 cups of batter) and this time add a teaspoon of orange food coloring. Put these two cakes in the oven to bake. Cover the mixing bowl of batter with plastic wrap and clean and dry the bowl you used for coloring.

Pro tip: Wrapping the cakes in plastic wrap while they are still slightly warm will make for softer edges, tops, and bottoms on the cooled cakes. Make sure to leave the parchment paper round on the bottom of the cakes for easier maneuvering later.

• Don’t rush: Bake the cakes one day and assemble 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. Your cake will have a more polished, professional look from this one maneuver.
• 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. This will make the opening look fuller as the candy falls out. Use coated candy and jimmy sprinkles for the longest-lasting candy filling. Chocolate and gummy candies sweat inside the cake.
• Don’t cut the cake right away: The cake will be sturdier after the frosting has set, making for a cleaner-slicing, easier-to-serve cake.

Here is my philosophy — invest your baking time in making the beautiful rainbow layers and make a basic buttercream. You can use your favorite recipe, but will need to double the amounts for filling and covering this cake.

Buttercream basics: How To Make a Basic Buttercream Frosting

You’ve got your baked cake layers; your buttercream frosting; and about two cups of sprinkles, coated candies, and edible glitter and now you must build the cake. Don’t panic! Decide in advance the order your layers will go in by stacking the wrapped cakes. And finally split your six cakes into three sets of two: bottom layers, middle layers, and top layers. The two middle layer cakes will get a hole in the middle.

Pick a cake plate and line it with parchment paper: Put a dab of frosting in the center of your cake plate. 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: Unwrap the purple cake layer and remove its parchment paper. Place it on the center of the cake plate. Top with 3/4 cup of frosting and smooth into an even layer. Some crumbs may stick into the frosting, but don’t worry — you won’t see them once the cake is complete. Unwrap the blue cake layer and remove the parchment paper round. Invert the blue layer on top of the purple layer, making sure to align the two cakes as much as possible. Frost the top of the blue cake layer with another 3/4 cup frosting.

Unwrap, punch holes, and stack the two middle layers: Unwrap the green cake layer, but keep the parchment round on. 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. Use the green cake’s parchment paper to easily invert the green cake over the blue layer. Peel away and discard the parchment paper. Frost the green ring with 1/2 cup of frosting, keeping clear of the hole for now. Repeat unwrapping, punching a hole, and moving to the stack of cakes with the yellow layer. Remove the yellow cake’s parchment paper and frost the yellow layer with 3/4 cup frosting. This time frosting the interior of the cake’s hole with a thin layer of frosting.

Fill the cake with sprinkles! Pour the sprinkles and candy into the cavity 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: Unwrap the orange cake layer and remove its parchment paper. Place the orange cake layer on top of the yellow cake layer and align the cakes as much as possible. Frost the top with 3/4 cup of frosting. Unwrap the red cake layer, remove the parchment, and level the cake if needed. Invert the red layer on top of the orange layer, making sure to align the two cakes as much as possible.

Crumb coat the cake: Place half 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. 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. Refrigerate the crumb-coated cake for one hour.

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. Top with any additional sprinkles, candies, and topping as desired.

Refrigerate the finished cake for at least one hour or even overnight before slicing and serving. Use a long, sharp knife to slice through the finished cake, and be prepared that the tip of the knife will meet some resistance as it goes through the sprinkles. You’ll also want a spoon to scoop some of the cake’s candy filling onto each plate.

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 candy may stick, so jostle the cake a bit to unleash the full cascade!