makes one 10 inch cake

1/2 cup butter, softened
1/2 cup shortening
3 cups sugar
6 eggs, separated
3 cups sifted cake flour
1/4 teaspoon baking powder
1/4 teaspoon baking soda
1/4 teaspoon salt
1 cup commercial sour cream

Cream butter and shortening; gradually add sugar, beating well. Add egg yolks, one at a time, beating after each. Combine flour, baking powder, soda and salt; add to creamed mixture alternately with sour cream, beginning and ending with flour mixture. Beat egg whites until stiff; gently fold into batter. Pour batter into greased and floured 10 inch tube pan. Bake at 325 degrees for 1 and 1/2 hours, or until a wooden pick inserted in center comes out clean. Cool in pan for 10 minutes; remove from pan and cool completely.