* Boneless, cut 1 inch thick. Combine onion, parsley, vinegar, oil, mustard, garlic and thyme. Place beef chuck shoulder steak in plastic bag; add marinade, spreading evenly over both sides. Close bag and marinate in refrigerator 6 to 8 hrs (or overnight, if desired, turning at least once. Pour off marinate; discard. Place steak on rack in broiler pan so meat is 3 to 4 inches from heat. Broil 16 to 18 min to doneness desired (rare to med.-rare), turning once. Carve steak into thin slices.