Preheat oven to 325°F. Grease a 12-cup Bundt pan with butter or shortening. Add about 2 tablespoons of flour and jiggle pan around so flour covers all of the buttered areas.
Cream butter and sugar. Beat in cream cheese, then add egg yolks and vanilla. Stir in flour by hand. Fold in stiffly beaten egg whites. Bake for one hour or until a toothpick inserted in middle comes out clean. Let cool and serve with powdered sugar sprinkled on top and fresh strawberries on the side, if desired.