-
In a large bowl mix together sugar, butter, lemon zest, lemonade, and vanilla on medium speed until combined, about 5 minutes. Add eggs and egg whites, one at a time, beating well after each addition.
-
In a medium bowl, combine flour, baking powder, salt, and baking soda. Add flour mixture and buttermilk alternately to sugar mixture, beginning and ending with flour mixture; beat well after each addition.
-
Pour batter into 2 – 9″ round cake pans coated with cooking spray; tap pans once each to remove air bubbles. Bake for 20 minutes, or until a toothpick inserted in the center comes out clean. Cool cake in pans for 10 minutes on a wire rack; remove from pans. Cool completely on wire rack.