Grilled London Broil And Onions

• 2 lb 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 tsp salt, divided
• 1/2 tsp black pepper
• 1/4 cup (1/2 stick) butter
• 4 medium-size sweet onions, thinly sliced

1. 1. Place the steak in a large resealable plastic storage bag.
2. 2. In a medium bowl, combine 1/2 cup vinegar, the oil, 1/4 cup mustard, the garlic, 1/2 tsp salt and the pepper, mix well. Pour over the steak then seal the bag and chill for 1 hour.
3. 3. Meanwhile, melt the butter in a large skillet over medium-high heat. Add the onions and saute for 12 to 15 minutes, or until very tender, stirring occasionally. Add the remaining 1/4 cup vinegar, 1/4 cup mustard and 3/4 tsp salt. Reduce heat to medium-low and cook until the mixture thickens, stirring often.
4. 4. Preheat the grill to high heat. Grill the steak for 12 to 15 minutes fo medium-rare, or to desired doneness beyond that, turning frequently; baste often with the marinade for only the first 5 minutes or cooking. Thinly slice the steak and serve topped with the sauteed onions.

steak, balsamic vinegar, olive oil, brown mustard, garlic, salt, black pepper, butter, sweet onions

Taken from www.epicurious.com/recipes/member/views/grilled-london-broil-and-onions-51790091 (may not work)