Cream butter and cream cheese; add sugar and beat until light and fluffy. Add egg yolks one at a time, beating well after each addition. Add flour gradually, and with the lowest speed of mixer, beat until well blended. Stir in Vanilla.
In a separate bowl, beat egg whites until stiff. Fold in cream-cheese batter.
Spoon into greased ad floured 10 inch tube pan. Bake at 325 degrees for 1 to 1 1/2 hours, or until toothpick inserted in center comes out clean and cake pulls away from sides of pan.
Cool in pan 10 minutes before turning out on a wire rack. Cool completely before slicing.