French Onion Stuffed Chicken Casserole

INGREDIENTS

2 tbsp

unsalted butter

large onions (halved and thinly sliced)

salt and pepper (to season)

2 tsp

fresh chopped thyme (divided)

2 tbsp

white wine, sherry or balsamic vinegar ((OPTIONAL))

2 cloves

garlic (minced)

1/2 cup

beef broth or stock (divided)

1 tbsp

olive oil

boneless, skinless chicken breasts

2 tsp

garlic powder

1 tsp

ground thyme

1 cup

shredded gruyere cheese ((or mozzarella cheese))

4 tbsp

freshly grated parmesan cheese