Looks Good: Super Epic Rainbow Cake

Courtesy Whisk Kid.

Ingredients
Cake:
2 sticks butter, room temp
2 1/3 c sugar
5 egg whites, room temp
2 teaspoons vanilla
3 c flour
4 tsp baking powder
½ tsp salt
1 1/2 c milk, warmed for 30 sec in microwave to bring to room temp
Red, orange, yellow, green, blue and purple food coloring

Buttercream Filling and Crumb Coat:
9 egg whites
1 ¾ c sugar
4 sticks of butter, room temp
2 tsp lemon extract

Frosting:
5 egg whites
1 c sugar
2 sticks butter, room temp
1 tsp lemon extract

Go to Whisk Kid for instructions.

(Thanks for the tip, Hrag.)