In a shallow bowl or resealable plastic bag, combine flour, season salt and pepper. Add steaks; dredge or toss to coat. In a skillet over medium heat, brown steak in 2 tablespoon of butter. Remove the steaks; spread each with 1/2 teaspoon mustard. Pour 1/4 teaspoon Worcestershire sauce over each; keep warm.
In the same skillet, saute the mushrooms and onion in remaining butter until tender. Add beef broth, parsley and remaining Worcestershire sauce. Return steaks to skillet; cover and simmer for 5-7 minutes or until meat is tender.