Flank Steak with Caramelized Onions and Balsamic Glaze with grain

2/3 cup balsamic vinegar 1 tablespoon olive oil 6 cups vertically sliced onion (about 1 1/2 pounds) 1/2 teaspoon salt, divided 1 (1-pound) flank steak,[...]

1/2 teaspoon salt 1/2 teaspoon black pepper 2 garlic cloves , minced 1 lb flank steak, trimmed cooking spray 6 cups onions , vertically sliced 1/2 cup blue[...]