Preheat oven to 325°F. Grease bottom of pans and line with waxed paper or parchment paper, or use Cake Release. (Click here for complete instructions on preparing baking pans.)
Sift together flour and baking powder. Set aside. Cream butter and sugar together until light and fluffy. Set aside. Beat egg whites until stiff, but not dry. Set aside. With mixer at slow speed, add flour mixture to butter mixture, alternately with milk. Beat well after each addition. Beat in vanilla extract. Gently fold egg whites into batter. Pour into prepared pans. Bake until toothpick inserted into center comes out clean.