Cream butter; gradually add sugar, beating well.
Combine flour, baking powder, and salt; add to the creamed mixture alternately with milk, beginning and ending with the flour mixture. Mix well after each addition. Stir in the flavorings.
Beat egg whites (at room temperature) until stiff peaks form; fold into batter.
Pour batter into a greased and floured 13- x 9- x 2-inch baking pan. Bake at 350° for 45 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 10 minutes; remove from pan, and let cool completely.
Cut cake into 2-inch squares; trim corners of each square, leaving rounded edges. Spread top and sides of each round with Fluffy White Frosting. Sprinkle coconut generously over frosting.