Pastel Layer Cake with Swiss Meringue Buttercream

Yields 20 servings

Source: Martha Stewart layer cake, Sprinkle Bakes frosting

Prep: 2 hours, total time about 4 hours


6 1/2 cups/789 g cake flour (not self rising), sifted

3 tablespoons baking powder

1/2 teaspoon fine grain sea salt

2 1/4 cups/500 ml whole milk

2 tablespoons pure vanilla extract

1 1/2 cups plus 4 tablespoons/395 g unsalted butter, room temperature

2 1/2 cups/490 g granulated sugar

10 large egg whites

A few drops of each: McCormick neon food color, in purple, green, pink and blue

and standard yellow and orange liquid or gel food color

Swiss meringue buttercream

12 egg whites

2 1/2 cups/500g sugar

1/4 teaspoon salt

2 1/2 pounds unsalted butter, softened

1 tablespoon clear vanilla extract

1 1/2 cups/ roughly 8 oz. assorted sizes of pastel confetti sprinkles

Star cake toppers and birthday candles

Make the cake layers: Preheat the oven to 350 degrees. Grease six 8-inch round cake pans, and line the bottoms with parchment. If you don't have six pans (understandably so) use as many as you have, and plan to wash them between baking cake layers.

Sift the flour, baking powder and salt into a large bowl. Combine milk and vanilla. Beat butter with a mixer on medium speed until smooth. With the mixer running, gradually add the sugar and beat until the mixture turns pale and fluffy, about 3 minutes.

Reduce speed to low, and add the flour mixture in 3 additions, alternating with the milk. Begin and end with the flour mixture. Beat until just combined. Do not over-mix.

Beat the egg whites in a clean mixer bowl on medium speed until stiff peaks form, about 5 minutes. Gently fold the egg whites into the batter in three additions.

Place two cups of batter in six separate bowls. Tint each bowl of batter with a little of the food color. Add food color a little at a time until the desired pastel tint is achieved. Fold the color in well with a rubber spatula until no streaks of white cake batter remains.

Spread the batter into the prepared pans and bake for 18 to 20 minutes. Let the layers cool completely on a wire rack. Run a knife around the edges of the cakes and the pans before turning them out.

Level the tops of the cake with a serrated knife or a cake leveler. Save the cake scraps for breakfast (smile). 

Make the frosting: Set a saucepan filled one-third full of water over medium-high heat and bring to a simmer.

Whisk together the egg whites, sugar, and salt in a large heatproof bowl ( I suggest a stainless bowl). Set over the simmering water and whisk until the mixture is hot to the touch and the sugar has dissolved (120-140 degrees on a candy thermometer, to be sure).

Transfer the mixture to the bowl of a stand mixer fitted with the whisk attachment.

Beat on low speed for 2 minutes. Increase to medium-high until stiff peaks are formed.

Continue beating at medium-high speed until the mixture is fluffy and has cooled (the mixing bowl should feel cool to the touch).

Turn the mixer off and switch from the whisk attachment to the paddle. Turn the mixer on medium-low and add the butter, a few cubes at a time, beating until well incorporated before the next addition.

Add the vanilla extract. Beat until the frosting on high speed until it is thick and completely smooth.

Important note about Swiss buttercream frosting! After a few pieces of butter are added to the whipped whites, the mixture will deflate. It may look like soup or even look curdled - do not let this discourage you. This is just one ugly stage the buttercream must pass through before becoming fluffy whipped frosting. You may read more about Swiss meringue buttercream here, and view my video tutorial.

Frost the cake: Transfer 2/3 cup of frosting to a piping bag fitted with a small star tip; set aside.

Fill each cake layer with 1/3 to 1/2 cup of the frosting. Begin with the violet cake layer on the bottom, followed by the blue, green, yellow orange and pink. Cover the entire cake with frosting using an off-set spatula. Place the cake in a large baking pan and toss on the confetti sprinkles, allowing the excess to fall back into the baking pan. Using the reserved frosting in the piping bag, pipe stars around the top edge of the cake and decorate each star with a large confetti sprinkle. Place the star toppers in the center of the cake, and add the birthday candles around the top edge of the cake near the piped stars.

Serve the cake: Cut a standard wedge of cake and divide it with a knife at the halfway point so that you have two pieces of cake. The first slice will be a triple layer of pink, orange and yellow, the second slice will be green, blue and violet. Or, divide the wedge into double layers, to serve three people. 

Cover the leftover cake loosely with plastic wrap and store at room temperature.