Skillet Steaks with Onion Gravy

1/2 C beef broth
4 Tbsp ketchup
1 tsp Worcestershire sauce
1 tsp Dijon mustard
1/8 tsp pepper
4 shell steaks (8oz each) (strip steaks, NY Strip, Kansas City Strip)
2 medium onions
2 Tbsp butter or margarine

Measure broth in large measuring cup; whisk in ketchup, Worcestershire sauce, mustard and pepper. Set aside. Heat large nonstick skillet over medium-high heat. Add steaks; cook 4 minutes on each side for medium. Remove steaks from skillet; cover and keep warm. Pour off fat from skillet. Thinly slice onions. Add butter to skillet and melt over medium heat. Add onions; cook stirring continually, about 3 minutes. Cover; reduce heat to medium low. Cook 5 minutes longer. Stir broth mixture into skillet; cook until heated through, about 2 minutes. Pour over steaks. Serve immediately.