Cream butter until soft and light. Gradually add sugar and continue creaming several minutes to incorporate as much as possible. Combine flour, baking powder and salt; sift 3 times. Add flavoring to milk and water. Add flour alternattely with liquid to creamed mixture; beat well after each addition. Beat egg whites until stiff, but not dry, fold immediately into batter, blending well, but do not beat. Pour into 3 greased and floured 23 cm layer pans. Bake at 180ºC for 25 minutes. Cool 5 minutes, then turn onto cooling racks and remove pans. When cool, fill and frost with Chocolate Frosting. Chocolate Frosting: Melt chocolate over hot water. Reserve. Combine remaining ingredients. Add some of the melted chocolate and beat in well. If desired, continue to beat in additional chocolate until desired chocolate color and flavor are obtained. Fills and frosts a 23 cm 3-layer cake. ----