In A Shallow Bowl Or Resealable Plastic Bag, Combine Flour, Salt And Pepper. Add Steaks; Dredge Or Toss To Coat. In A Skillet Over Medium Heat, Brown Steak In 1 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 Parsley And Remaining Worcestershire Sauce. Return Steaks To Skillet; Cover And Simmer For 5-7 Minutes Or Until Meat Is Tender.