Rainbow Birthday Cake

My baby girl turned one last week!  It's still crazy to think that one year has gone by already!  Anyway, I decided quite a while ago that I wanted to do a rainbow themed birthday for her.  I was constantly looking at pinterest for fun ideas, which of course there were a ton, but my favorite was the rainbow cake.  It was so visually striking that I just couldn't resist giving it a try.  Since the cake was so huge I resisted the urge to go out and buy about 50 rainbow snacks just to make things even more rainbow colored, which was good because everyone just ate the cake anyway.  

This cake was so fun to make, but I'll be honest with you, it takes a long time to make.  It took me almost 5 hours to make from start to finish, but it was well worth it to have it turn out for my girl.  No one at the party had any idea what it looked like inside and so when I pulled out the first slice of cake everyone was amazed!  They all raved about how delicious it was as well.(Which it should be for how much butter is in it!)  So I'd call this cake adventure a success!    

Rainbow Cake

Makes 6 6" round cakes

Cake ingredients
10 large egg whites, room temperature
1 1/2 cups whole milk, room temperature
4 1/2 tsp vanilla
5 1/2 cups flour
3 1/2 cups sugar
3 Tbsp baking powder
1 1/2 tsp salt
1 1/2 cups (3 sticks) unsalted butter, room temperature, cubed
red, yellow, green, & blue food coloring

Icing  (Makes 5 cups) (I doubled this recipe for my cake)
4 cups powdered sugar
10 Tbsp butter, room temperature
4 Tbsp milk
1 tsp vanilla

Preheat oven to 350 degrees F.  In a bowl combine the egg whites, 1/2 cup milk, and vanilla with a wire whisk.  Set to the side.  In a separate bowl, mix the flour, sugar, baking powder, and salt, with a hand mixer on low speed until ingredients are combined.  Add the butter and the remaining 1 cup of milk to the flour mixture.  Mix on low speed until all ingredients are moistened.  Increase the speed to medium and mix for 1 1/2 minutes.  The batter should start to stick to the beaters.  Add the milk/egg mixture in 5-6 separate batches, mixing until combined, approximately 20 seconds each batch.  Separate the cake batter into 6 bowls.  Add enough food coloring to make one red, orange, yellow, green, blue, and purple cake.  Next, spray the cake pans with cooking oil and then sprinkle with flour.  If you only have a couple of cake pans, you made need to bake in batches.  Bake for 15-20 minutes or until a toothpick comes out clean.  Remove the pans from the oven and let cool for 10 minutes.  Remove the cake from the pans, and let cool on a wire rack.  Continue the process until all 6 cakes are done.  Once the cakes have cooled, wrap them in Saran Wrap and place in the freezer for one hour.  They will be much easier to handle when icing.  To make the icing, beat the powdered sugar, and butter until smooth.  Add the vanilla to the milk.  Slowly drizzle in the milk and beat on high speed for 5 minutes until light and fluffy.  With a piece of cardboard, trace a 6" circle.  Place the purple cake on top of the cardboard and top with a layer of icing.  Continue layering with the blue, green, yellow, orange, and then red cake with icing in between.  Cover the top and sides with icing and then decorate as desired.