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.