1 (2-pound) London broil (beef top round) steak
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 teaspoon 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.
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