Flank Steak with Carmelized Onions and Balsamic Glaze

2/3 cup balsamic vinegar 

1 tbsp olive oil 

6 cups vertically sliced onion (about 1 ½ lbs) 

½ tsp salt, divided 

1 lb flank steak 

¼ tsp freshly ground black pepper 

¼ tsp dried thyme 

Bring balsamic vinegar to a boil in a small sauce pan. Reduce heat to medium, cook until reduced to about ¼ cup. Remove from heat. 

Heat oil in large non-stick skillet over medium-high heat. Add onion and sauté for 10 minutes or until tender. Sprinkle with ¼ tsp salt, sauté 18 minutes or until onions are golden brown. Remove from heat.

Preheat broiler

Sprinkle steak with remaining ¼ tsp salt, pepper and thyme. Places steak on broiler pan coated with cooking spray, broil 6 minutes on each side until desired doneness. Serve onions over steak and drizzle with balsamic glaze.