French Onion Chicken Skillet

Ingredients

• 2 pounds Vidalia onions, sliced
• 2 pounds boneless, skinless chicken breasts or thighs
• 2 cups beef broth
• 1 cup swiss cheese, grated
• 1/3 cup extra-virgin olive oil, divided
• 2 tablespoons all-purpose flour
• 2 teaspoons balsamic vinegar
• 1/2 teaspoon dried thyme
• 1/2 teaspoon dried sage
• Kosher salt and freshly ground pepper, to taste