The Ultimate Birthday Bash Funfetti Layer Cake

Preheat oven to 350°F (175°C). Grease, line the bottoms with parchment paper, and flour two 8-inch cake pans.

In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.

In a large bowl, beat the softened butter and granulated sugar together until pale and fluffy (about 3 minutes).

Beat in the 4 egg yolks one at a time, mixing well after each addition. Stir in the vanilla extract.

Combine the milk and buttermilk. Gently mix the dry ingredients and the wet liquids into the butter mixture in three alternating additions, beginning and ending with the dry ingredients. Mix just until combined; do not overmix.

In a separate, clean bowl, whip the 4 reserved egg whites until stiff, glossy peaks form.

Gently fold the whipped egg whites into the main batter in two additions until just incorporated. Then, gently fold in the rainbow sprinkles, being careful not to overmix.

Divide batter evenly between the prepared pans. Bake for 30–35 minutes, or until a toothpick inserted into the centre comes out clean.

Let cakes cool in the pans for 10 minutes, then invert onto wire racks to cool completely.

To make the frosting, beat the softened butter in a stand mixer until smooth. Gradually add the sifted confectioners' sugar.

Mix in the vanilla and salt. Slowly add the heavy cream/milk, one tablespoon at a time, beating on medium-high until the frosting is light and fluffy.

Once cakes are completely cool, level the tops if necessary. Place the first layer on the serving plate and spread a thin layer of frosting (the crumb coat). Chill for 15 minutes.

Place the second layer on top. Cover the entire cake with the remaining buttercream and decorate as desired.