How to Make Instagram's Famous Rainbow Explosion Cake

Food Network Magazine caught up with Flour Shop Bakery owner Amirah Kassem to learn how to make the most Instagrammable cake of all time. FYI — you're going to need a lot of sprinkles.

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September 10, 2019
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Not Your Average Birthday Cake

When Amirah Kassem was in the throes of opening her New York City bakery, Flour Shop, she took a break one afternoon to bake a cake for a friend’s son’s birthday. She’d made plenty of cakes for friends in the past, but this time was different: After she baked a full set of bright rainbow cake layers, she cut a hole in the center of each and filled the inside of the cake with multicolored sprinkles. She imagined an explosion of sprinkles when the cake was cut — like an edible version of all the piñatas she’d seen at parties while growing up in Mexico. “When the birthday boy sliced it open, it was a total paparazzi moment,” Amirah says. “Everybody pulled out their phone to take a picture.” Realizing she had a hit on her hands, she added the creation to the Flour Shop menu, and the cake exploded again — on Instagram. Famous fans like Beyoncé, Katie Holmes and Kelly Ripa shared photos of it, and Instagram called out rainbow and unicorn cakes as a top trend, using a Flour Shop cake as an example. Amirah shared the recipe (from her book, The Power of Sprinkles) so you can make one yourself!

Photographs by Henry Hargreaves

Buy It: The Power of Sprinkles Cake Book: Amazon, $13.44

Cut Out the Center

Use a 2-inch round cookie cutter to carefully cut the center out of every cake except the top pink one. Wipe the cookie cutter in between each cut so you don’t transfer one cake color to the others.

Get the Recipe: Bonilla Vanilla Cake

Build Your Base

Build the cake on a base that’s at least 2 inches bigger than the cakes (a disposable cake board, a plate, a cake stand or a flat platter). Using a piping bag, make a small ring of frosting on top of the board in roughly the same shape as the cake ring. This is so that the cake sticks to the base.

Purple Goes at the Bottom

Put the bottom purple cake layer on top of the frosting. Using a piping bag, cover the cake with an even layer of frosting, leaving a little room around the hole. (You don’t want to get frosting in the hole, or your sprinkles explosion will stick to the frosting.)

Get the Recipe: Magical Frosting

Layer, Pipe and Repeat!

Alternate adding cake and frosting (pipe the same amount of frosting for each layer), working in this order: purple, blue, green, yellow and orange. Eyeball it from the top as you go to make sure the holes line up. It’s easier to adjust as you go rather than fix a tilting six-layer cake at the end!

Pour in Your Sprinkles

Wait! Don’t add the top layer of cake just yet. Pour 1 3/4 cups assorted rainbow sprinkles into the hole (a scoop or a measuring cup with a spout works perfectly). Pat down the sprinkles to the height of the cake and frosting.

Top Your Cake

This is it, the sixth and final layer! Flip the last layer, the pink one, upside down so you have a flat surface to frost and place it on the cake.

Frost the Outside of Your Cake

Apply a thin layer of frosting all around the cake using a spatula, the dull side of a butter knife or an offset spatula. This is a crumb coat. The point is to seal in the crumbs, fill in a solid layer of white between the layers and protect the cake from drying out. Refrigerate the cake for a little bit at this point so that the cake doesn’t begin to slip and slide around or start to tilt.

Don't Forget Your Sprinkle Coating

Cover the cake in a final layer of frosting (it doesn’t have to be thick). Move the cake (on the board) to a baking sheet. With dry hands, scoop up some rainbow nonpareils and then start moving your hand up along the side of the cake, working from the bottom to the top, until the cake is covered. If you feel comfortable, tilt the cake as you work by holding it under the base.

The Big Reveal

For the big reveal, cut a large first slice to maximize the sprinkles explosion effect! When cutting the rest of the slices, wipe the knife after each slice so one color doesn’t transfer to the others.

Buy the Cake Kit

Flour Shop's Rainbow Explosion Cake Kits are also available now at Williams-Sonoma. Each kit comes with cake and frosting mix, food coloring, assorted sprinkles for the cake's center and rainbow nonpareils for decorating the cake's outer layer.

Buy It: Williams Sonoma, $59.95