White part: Beat egg whites until foamy, then add cream of tartar and contiune beating until eggs hold a point. Add sugar gradually and continue beating. Fold in flour which as been sifted with salt. Add lemon flavoring and place mixture in a large ungreased tube pan.
Yellow part: Beat egg yolks until light and fluffy. Add sugar gradually and continue beating. Add flavoring, then alternate adding boiling water and flour which has been sifted with baking powder and salt. Mix smooth and pour batter over the white batter.
Bake in a moderate oven (350° F) for about 40-50 minutes. Invert cake to cool, then remove cake and serve plain or ice as desired.