1. Sprinkle steaks on both sides with pepper and salt; set aside. In a large skillet, cook onion and mustard in 2 tablespoons butter for 1 minute. Add steaks; cook for 2-5 minutes on each side or until the meat reaches desired doneness (for medium-rare, a meat thermometer should read 145°; medium 160°; well-done 170°).
2. Remove steaks to a serving platter and keep warm. In the same skillet, add the lemon juice, Worcestershire sauce and remaining butter; cook and stir for 2 minutes or until thickened. Add parsley and chives. Serve with steaks. Yield: 4 servings.