Classic French Onion Soup

1/4 c butter
3 large yellow onions, sliced
1 c dry white wine
3 cans beef or chicken broth
1 tsp worchestershire sauce
1/2 tsp salt
1/2 tsp dried thyme leaves
4 slices french bread, toasted
1 c shredded swiss cheese

Melt butter in skillet over medium.Add onions and cook 15 mins or until soft and light brown. Stir in wine. Combine onion mixture, broth, Worcestershire sauce, salt and thyme in crockpot. Cover and cook on low 4-41/2 hrs. Ladle soup in to bowls, top with bread and swiss cheese.