Rainbow Birthday Cake

Preheat the oven to 350°F (175°C). Grease and flour three 9-inch round cake pans, then line the bottoms with parchment paper. (5 minutes)

In a large bowl, cream together the softened butter and sugar until light and fluffy using an electric mixer. (7 minutes)

Beat in the eggs one at a time, then stir in the vanilla extract. (3 minutes)

In a separate bowl, whisk together the flour, baking powder, and baking soda. Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix until just combined. Be careful not to overmix. (10 minutes)

Divide the batter evenly among three bowls. Tint one bowl red, one yellow, and one blue using gel food coloring. (5 minutes)

Pour each batter into the prepared cake pans and spread evenly. (3 minutes)

Bake for 25-30 minutes, or until a wooden skewer inserted into the center comes out clean. (30 minutes)

Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely. (10 minutes)

While the cakes are cooling, prepare the buttercream frosting. In a large bowl, beat the softened butter with a pinch of salt until smooth. Gradually beat in the sifted confectioners' sugar, alternating with the heavy cream, until light and fluffy. Stir in the vanilla extract. (10 minutes)

Divide the buttercream frosting into three bowls. Tint one bowl orange, one green, and the other purple using gel food coloring. (5 minutes)

Once the cakes are completely cool, level the tops if necessary. Place the red cake layer on a serving plate and spread with the orange buttercream frosting. Top with the yellow cake layer and spread with the green buttercream frosting. Add the blue cake layer and cover it with the purple buttercream frosting. (10 minutes)

Refrigerate the cake for at least 30 minutes to allow the buttercream to set. (30 minutes)

While the cake is chilling, prepare the Fluffy Icing. In a saucepan, bring the corn syrup to a boil. (5 minutes)

In a heatproof bowl set over a simmering pot of water (double boiler), beat the egg whites and cream of tartar together until frothy. (3 minutes)

Slowly pour the hot corn syrup into the egg white mixture, beating constantly until stiff, glossy peaks form. Remove from heat and beat in the vanilla extract. (7 minutes)

Generously frost the chilled cake with the Fluffy Icing. Swirl and create peaks with a spatula or spoon. (5 minutes)

Serve immediately and enjoy!