Ingredients
3 cups of my GF cake mix blend (see below)4 tsp baking powder
½ tsp salt
2 sticks butter, room temperature
2? cup sugar
5 large egg whites, room temperature
2 tsp vanilla extract
1½ cups milk, room temperature
Gel food coloring (not liquid, it's not vibrant enough!)
Vanilla buttercream icing (I used the one straight out of my red Betty Crocker cookbook but honestly between you and me no one has to know if you just buy a can of frosting - go on, you deserve it after all the hard work the cake has been!)
Marshmallow Icing
Preparation
1.Preheat oven to 350 degrees. Brush six 9" round pans with shortening. Line bottom with parchment paper. DO NOT SKIP THIS STEP. Brush again with shortening.
2.Whisk together GF cake mix flour, baking powder, and salt. Set aside.
3.Cream butter and sugar. Slowly add egg whites then vanilla.
4.Alternate mixing in the flour mix and the milk beginning with the flour and ending with the milk. Beat 2 minutes.
5.Divide batter between 6 bowls. Add food color to each bowl until it's the hue you desire. The way the cake batter looks is just about how your baked cake will look.
6.Transfer each color to individual cake pan (if you don't have 6 pans be sure to put the ones you're not baking into the fridge).
7.Bake 15 minutes until toothpick comes out clean in the center. Let cool 10 minutes then invert onto wire rack. Let cool completely.
8.Trim tops of cake to make level.
9.Place purple layer on cake plate. Spread scant 1 cup of buttercream frosting so it extends just beyond the edges.
10.Repeat with blue, green, yellow, orange, and red.
11.Place in fridge for 30 minutes then cover top and sides with marshmallow icing.