Preheat oven to 350 degrees F. Grease and flour 2 six -nch round cake pans.

Mix together the flour, baking powder, baking soda and salt. Set aside.

Combine sugar, softened butter, lemon zest, lemonade concentrate and vanilla in a mixing bowl and beat until light and creamy. Add egg and beat for 30 seconds, then beat in the egg white. Mixture may looks a little curdled at this point, but it will smooth out after you add the dry ingredients and milk.

With a spoon, stir in half of the flour mixture until blended, then stir in half of the milk. Continue adding remaining flour mixture and milk alternately, stirring until fully blended.

Divide the batter between the two pans. Set on a baking sheet and bake at 350 for 25 minutes (check at 20). The cakes will be fairly flat with golden brown edges. Loosen gently from the sides and let cool in pans for about 10 minutes, then carefully turn from the pans.

To make the frosting, beat the butter, lemon rind, lemonade concentrate, vanilla and cream cheese together. Gradually add the powdered sugar until mixture is creamy. If frosting feels too soft, refrigerate it briefly before spreading.