French Onion Chicken

Description:

Ingredients:

3 tablespoons unsalted butter
2 pounds onion (sliced)
2 cloves garlic (minced)
1 teaspoon fresh thyme leaves (chopped)
2 tablespoons flour
2 cups low-sodium or unsalted beef broth
1 tablespoon olive oil
1 pound bone-in chicken thighs (3 thighs)
2 teaspoons balsamic vinegar
2 tablespoons Dijon mustard
1 cup gruyere (grated)
salt
ground black pepper