Cream butter and 1 1/2 cups sugar until light and fluffy; beat in egg yolks one at a time. Fold in beaten egg whites. Sift together flour, baking powder, baking soda and salt, and add to batter a little at a time, alternating with sour cream.
Stir until smooth. Mix in grated orange peel and walnuts and pour into buttered 9 inch tube pan. Bake 50 minutes at 350° F. Mix remaining sugar with orange juice and Amaretto and spoon over cake as soon as it comes out of oven.
Cool before removing from pan.Servings: