What You’ll Need:
- 1 (2-pound) London broil steak (beef top round)
- 3/4 cup balsamic vinegar, divided
- 1/4 cup olive oil
- 1/2 cup spicy brown mustard, divided
- 2 cloves garlic, minced
- 1 1/4 teaspoons salt, divided
- 1/2 teaspoon black pepper
- 1/4 cup (1/2 stick) butter
- 4 sweet onions, thinly sliced
What To Do:
- Place steak in a large resealable plastic bag.
- In a medium bowl, combine 1/2 cup vinegar, the oil, 1/4 cup mustard, the garlic, 1/2 teaspoon salt, and the pepper; mix well. Pour over steak then seal bag and chill 1 hour.
- Meanwhile, in a large skillet over medium-high heat, melt butter. Add onions and saute 12 to 15 minutes, or until very tender, stirring occasionally. Add remaining vinegar, mustard, and salt. Reduce heat to medium-low and cook until mixture thickens, stirring often.
- Preheat grill to high heat. Grill steak 12 to 15 minutes for medium-rare, or to desired doneness beyond that, turning frequently; baste often with marinade during only the first 5 minutes of cooking. Thinly slice steak against the grain and serve topped with sauteed onions.