Sift flour once, measure, add baking powder, and sift
together three more
time.
Cream butter thoroughly, add sugar gradually, and cream
together until
light and fluffy.
Add flour, alternately with liquid, a small amount at
a time. Beat after
each addition until smooth.
Add vanilla; fold in egg whites.
Bake in greased pan, 11x7x2 inches, in moderate oven
(325 degrees) 50
minutes, or until done.
Spread with seven Minute Frosting.