Preheat oven to 350 degrees.
Grease 2- 8" round cake pans & then line the bottom with parchment, then grease the parchment - set aside.
Combine egg whites, milk & vanilla in a large measuring cup & whisk together with a fork - set aside.
In a large bowl, sift together flour, sugar, baking powder & salt.
Beat in cubes of butter until crumbly.
Pour in 1/2 cup of the milk mixture & beat well for about 90 seconds.
Add remaining milk & beat again for 60 seconds.
Fold in rainbow jimmies.
Pour batter evenly between the 2 prepared pans.
Bake 30-40 minutes or until toothpick test is clean.
Cool completely before frosting. (I like to freeze them.)