Vibrant Rainbow Birthday Cake

Follow our step-by-step guide on how to make Vibrant Rainbow Birthday Cake.

1. Step 1

   Preheat your oven to 350°F (175°C). Grease the sides of three 9-inch round cake pans and line the bottoms with parchment paper.

2. Step 2

   In a large bowl, beat the softened butter and white sugar together using an electric mixer until the mixture is fluffy and light in color.

3. Step 3

   Add the eggs one at a time, mixing well after each addition. Then, stir in the vanilla extract.

4. Step 4

   In a separate bowl, combine the all-purpose flour, baking powder, and baking soda. Gradually add this dry mixture to the butter mixture, alternating with the buttermilk. Start and end with the flour mixture, making three additions of flour and two of buttermilk.

5. Step 5

   Divide the batter evenly among three bowls. Tint one bowl with red food coloring, one with yellow, and one with blue. Mix until the colors are well incorporated.

6. Step 6

   Pour each colored batter into the prepared cake pans, smoothing the tops with a spatula.

7. Step 7

   Bake in the preheated oven for about 30 minutes, or until a toothpick inserted into the center comes out clean. Allow the cakes to cool in the pans for 15 minutes before running a knife around the edges to loosen them. Turn the cakes out onto a wire rack, peel off the parchment paper, and let them cool completely for about 30 minutes before frosting.

8. Step 8

   For the buttercream icing, beat unsalted butter and a pinch of salt in a large bowl until smooth. Gradually add confectioners' sugar and cream, alternating between the two, until well combined. Mix in the vanilla extract.

9. Step 9

   Divide the buttercream icing into three bowls. Tint one bowl orange, one green, and the other purple.

10. Step 10

    To assemble the cake, place the red layer on a flat serving plate and spread the top with orange icing. Add the yellow layer and spread green icing on top. Finally, place the blue layer on top and cover it with purple icing. Refrigerate the cake for 30 minutes to firm up the icing.

11. Step 11

    For the fluffy icing, bring corn syrup to a boil in a saucepan. In a heat-proof bowl set over simmering water, beat egg whites and cream of tartar until frothy. Gradually add the hot corn syrup in a thin stream while continuing to beat until stiff peaks form. Remove from heat and mix in vanilla extract. Spread this fluffy icing over the top of the cake.