Flank Steak with Triple-Grilled Onions

INGREDIENTS

1 1/4 lb

Flank steak, lean

Onion(s) yellow, cut into 1/2-inch-thick slices, medium

Red onion(s) cut into 1/2-inch-thick slices, medium

Vidalia onion(s) cut into 1/2-inch-thick slices, large

4 1/2 tsp

Balsamic vinegar

1/4 tsp

Black pepper, freshly ground

1 tsp

Table salt

3 tbsp

Unpacked brown sugar