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Cook for 15 minutes or until inserted toothpick comes out clean.  Let cakes cool.

Make frosting and assemble cake.  Place waxed paper or parchment paper 

at the base to keep serving area clean. 

Crumb coat the cake and let cool in refrigerator for one hour.  

This will ensure no crumbs on the final layer of frosting. 

The final cake.  It is so unassuming and monochromatic (except for the sprinkles on the top)

Look at it now!  So colorful and delicious. Just looking at it puts a smile on your face. Thanks to my eager kids for helping decorate this cake.

Makes one 9-inch-round six-layer cake.

Vegetable shortening

3 cups all-purpose flour

4 tsp baking powder

1/2 tsp salt

2 sticks (1 cup) unsalted butter, softened

2 1/3 cups sugar

5 large egg whites, room temperature

2 tsp vanilla extract

1 1/2 cups milk

red, orange, yellow, green, blue, and purple gel food coloring

Swiss Meringue Buttercream (or your choice of frosting)

Preheat oven to 350 degrees.  Brush six 9-inch-round cake pans with shortening.  Line bottom of each cake pan with parchment paper; brush again and set aside.

In a large bowl, whisk together flour, baking powder and salt' set aside.  In the bowl of an electric mixer fitted with the paddle attachment, cream together butter and sugar.  Slowly add egg whites and mix until well combined.  Add vanilla and mix until fully incorporated.  Add flour mixture and milk in two alternating additions, beginning with the flour and ending with the milk.  Mix until well combined.

Divide batter evenly between six medium bowls.  Add enough of each color of food coloring to each bowl, whisking until desired shade is reached.  Transfer each color to an individual cake pan.  Transfer to oven and bake until a cake tester inserted into the center of each cake comes out clean, about 15 minutes (working in batches if necessary).

Remove cakes from oven and transfer to a wire rack; let cool for 10 minutes.  Invert cakes onto a wire rack; re-invert and let cool completely.

Using a serrated knife, trim tops of cakes to make level.  Place four strips of parchment paper around perimeter of a serving plate or lazy susan.  Place the purple layer on the cake plate.  Spread buttercream filling over the first layer with a small offset spatula so it extends just beyond edges.  Repeat process with blue, green, yellow, and orange layers.

Place the remaining red layer on top, bottom-side up.  Gently sweep away any loose crumbs with a pastry brush.  Using an offset spatula, cover the top and sides with a thin layer of frosting.  Refrigerate until set, about 30 minutes to one hour.

Using an offset spatula, cover cake again with remaining frosting.  Printable recipe

9 large egg whites

1 3/4 cups sugar

2 cups (4 sticks) unsalted butter, cut into small pieces, room temperature

2 teaspoons vanilla (or lemon) extract

Cook egg whites and sugar in a small saucepan over medium heat, whisking constantly until sugar is completely dissolved.  Transfer to the bowl of an electric mixer fitted with the whisk attachment; mix on high speed until mixture is room temperature. (it will start looking white and glossy) With the mixer on medium-low, add butter, one piece at a t time, mixing well after each addition (it is very important to use unsalted butter).

Remove whisk attachment and switch to paddle attachment.  Increase speed to high and beat until buttercream comes together, about 5 minutes; beat in vanilla extract.  Printable recipe