Directions

1. Coat grill rack with nonstick cooking spray. Preheat grill to medium (300°F to 350°F). Season steak with coarsely ground pepper to taste. Grill steak, uncovered, 14 to 18 minutes for medium rare or to desired doneness, turning once.
2. Meanwhile, in large skillet cook onions in butter over medium heat 13 to 15 minutes, stirring once. Season with salt to taste; add garlic. Cook 3 to 4 minutes more or until onions are caramelized. Add broth, vinegar, sugar and mustard. Bring to boiling; boil gently 3 to 5 minutes or until liquid evaporates.
3. To serve, cut steak into serving-size pieces and spoon onions over steak.