Rainbow Cake Ingredients :
- 3 cups all-purpose flour
- 4 teaspoons baking powder
- 1/2 teaspoon salt
- 1 cup unsalted butter at room temperature
- 2 1/3 cups sugar
- 4 large egg whites at room temperature
- 2 teaspoons pure vanilla extract
- 1 1/2 cups milk at room temperature
vegetable shortening and parchment paper for preparing the pan
Buttercream and Frosting Recipe
for the filling
- 9 large egg whites
- 1 3/4 cups white granulated sugar
- 2 cups unsalted butter, cut into small pieces, room temperature
- 1 teaspoon vanilla
for the frosting
- 4 large egg whites
- 1 cup white granulated sugar
- 1 cup unsalted butter, cut into small pieces, room temperature
Rainbow Cake Instructions
Preheat oven to 350 degrees. For this recipe you will need 9-inch-round cake pans. This cake has 6 layers so if you have 6 cake pans use those otherwise re-use the same cake pan as necessary. Line the bottom of each cake pan with parchment paper and brush with vegetable shortening.
In a large bowl, whisk together flour, baking powder and salt and set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream together butter and sugar. Slowly add egg whites and mix until well combined. Add vanilla and mix until fully incorporated. Add flour mixture and milk in two alternating additions, beginning with the flour and ending with the milk.
Divide batter evenly between six medium bowls. Add enough of each color of food coloring to each bowl, whisking, until desired shade is reached.
Transfer each color to an individual cake pan. Transfer to oven and bake for 10-15 minutes then remove the cakes and transfer to a wire rack and let cool for at least 10 minutes.
Make the butter cream by cooking the egg whites and the sugar in a small saucepan over medium heat, whisking constantly until sugar is completely dissolved. Then transfer to the bowl of an electric mixer fitted with the whisk attachment; mix on high speed until the egg whites peak. With the mixer on medium-low, add butter, one piece at a time, mixing well after each addition. Then remove the whisk attachment and switch to the paddle attachment. Increase speed to high and beat until buttercream comes together, about 5 minutes; beat in vanilla extract.
Spread a scant ½-1 cup buttercream filling over the first layer of the cake with a spatula so it extends just beyond edges. Repeat process with blue, green, yellow, and orange layers.
Make the frosting by repeating step number 6.
Place the remaining red layer on top. Using an offset spatula, cover the top and sides with a thin layer of frosting. and refrigerate until set, about 30 minutes.
