1. Preheat your oven to 350 F (175 C). Grease a casserole dish and season your chicken breasts.
2. In a mixing bowl, mix the white wine (or the milk) with the can of cream of onion soup. Add a couple of spoonfuls of the soup and wine mixture to the casserole and spread it. Arrange your chicken breasts and cover each one of them with a slice of the cheese.
3. Pour the rest of the soup and wine mixture over the chicken and the cheese.
4. Pour the stuffing mix over the casserole and sprinkle it with the butter.
5. Cover the dish with foil and bake for 35 minutes. Remove the foil and bake for 10-15 more minutes or until golden brown.
Pro tip: If you're going to freeze this casserole, it's better not to add the stuffing and add it whenever you're going to eat it. That way the bread won't get soggy while it thaws. In any case, serve over rice or with a side of steamed green beans.