1. In 12-inch skillet over medium-high heat, in hot butter or margarine, cook filet mignon until underside of meat is browned, about 4 minutes; turn meat and cook about 5 minutes longer for rare. Remove meat to warm platter; keep warm.
2. Reduce heat to medium. To drippings in skillet add vermouth and green onions; cook 2 minutes, stirring to loosen brown bits on bottom of skillet. Stir in water and remaining ingredients except watercress; heat to boiling.