Cut steak into very thin slices. Lightly quick fry in hot oil. Remove and add butter to skillet. Sauté onions and mushrooms. Remove and add butter if necessary to make 1
tbsp. Blend in flour. Cook until frothy. Blend in remaining ingredients all but sour cream. Simmer till thick and smooth. Add beef, heat, add sour cream, heat (do not boil.... it
will separate). Serve over simple rice.