Preheat the oven to 350ºF. Prepare a cupcake pan by inserting cupcake liners.
In a large mixing bowl, cream butter and sugar together.
Add milk and 2 cups of flour alternately, mixing in between. Add remaining cup of flour and baking powder. Beat well.
In a small mixing bowl, beat egg whites until peaks form.
Add egg whites to batter and beat well.
Split batter into 2 bowls. Add red food coloring to one bowl and blue food coloring to the other. The amount will depend on the time of coloring you are using.
Using a spoon, alternate red and blue scoops in each of the cupcake liners, filling them about ⅔ of the way full.
Bake for 20 minutes or until a toothpick comes out clean. Allow cupcakes to cool completely before frosting.
To make frosting, beat butter and powdered sugar together. Mixture will be crumbly.
Add vanilla and 2 tablespoons of milk. Beat well. If the frosting is too thick, add a bit more milk. If the frosting is too thin, add a bit more powdered sugar.
Put frosting in a large ziplock bag. Cut a small corner off and pipe frosting onto the cupcakes.
Add sprinkles and enjoy.
Notes
We like to use gel food coloring for this recipe.
You can cut it in half to make a smaller batch.
These can be frozen, see above on how to do that.
Switch up the food coloring for different holidays or occasions.