Allow all ingredients to come to room temperature first.
Cream the butter and sugar with the paddle attachment for
about 5 min. Until fluffy.
Meanwhile, sift the baking powder, salt, and flour(3 times).
Combine egg whites, milk, and vanilla together.
Once butter is creamed well, add 1/3 of dry ingredients until
combined well, 1/2 of wet, 1/3 of dry, rest of wet, and then
Pour immediately into wax paper lined pan. Bake @ 350 for
25-35 min. Depending on oven.