GRILLED LONDON BROIL
Serves: 6 to 8

One 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 garlic cloves, minced
1 1/4 teaspoons salt, divided
1/2 teaspoon black pepper
1/4 cup (1/2 stick) butter
4 medium-size sweet onions, thinly sliced

Place the steak in a large resealable plastic storage 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 the steak, then seal the bag and chill for 1 hour. Meanwhile, melt the butter in a large skillet over medium-high heat. Add the onions and sauté for 12 to 15 minutes, or until very tender, stirring occasionally. Add the remaining 1/4 cup mustard, 1/4 cup vinegar, and 3/4 teaspoon salt. Reduce the heat to medium-low and cook until the mixture thickens, stirring often. Preheat the grill to high heat. Grill the steak for 12 to 15 minutes for medium-rare, or to desired doneness, turning frequently; baste often with the marinade for only the first 5 minutes of cooking. Thinly slice the steak and serve topped with the sautéed onions.