Cream butter, gradually stir in 1/2 cup icing sugar, beating until smooth. Beat egg whites until stiff but not dry; gradually beat in 1 cup icing sugar. Combine both mixtures and continue adding icing sugar until of good spreading consistency. Add desired flavoring and food coloring. Frosting should be stiff enough to hold its shape. Good for decorating cakes. YIELD: Enough for large layer cake.