Mix together the powdered sugar, butter, egg yolks, and vanilla. Combine flour and baking powder. Add dry ingredients to creamed mixture, alternating with milk and mix well. Fold in coconut. Beat egg whites until stiff and fold into batter. Pour into greased 9 x 13" baking pan. Bake at 350 degrees for 30 minutes. Frost with your favorite cream cheese icing. ENJOY!