Sift flour once, measure, add baking powder and salt, and sift together three times. Cream butter thoroughly, add sugar gradually, and cream together until light and fluffy. Add flour, altemately with milk, a small amount at a time, beating after each addition until smooth. Add flavoring. Fold in egg whites quickly and thoroughly. Bake in three greased 9-inch layer pans in moderate oven ( 375 degrees F.) 20 to 25 minutes. Spread Chocolate Cream Filling (see recipe) between layers and Hungarian Chocolate Frosting (see recipe) on top and sides of cake. When frosting is set, write numbers from one to twelve around top of cake with white frosting to represent the face of a clock. Place hands of clock at twelve o'clock.