buttermilk and vanilla, then add the other half of the dry ingredients. the mixture should be fluffy but relatively thick.
in a glass or metal bowl, beat the 4 egg whites at high speed until they have soft peaks.
add remaining 1/4 c sugar and beat until mixture has stiff peaks.
using a rubber spatula, gently fold 1/3 of the egg white mixture into the batter, in order to lighten the batter. fold in remaining egg whites just until any trace of egg white disappears. batter should be lighter in color and texture at this point.
gently and evenly divide the batter into prepared pans, smooth tops, and bake 40-50 minutes, until cake pulls 