It's been a few years since I made this, but I remember it being very good. It's from Extra-Special Crockery Pot Recipes by Lou Seibert Pappas.
French Onion Soup
4 large yellow onions, thinly sliced
1/4 cup butter
3 cups rich beef stock
1 cup dry white wine
1/4 cup medium dry sherry
1 tsp Worcestershire sauce
1 clove garlic, minced
4-6 slices buttered French bread
1/4 cup grated Romano or Parmesan cheese or dry Jack cheese
Using a large frying pan, slowly saute onions in butter until limp and glazed. Transfer to crockery pot. Add beef stock, white wine, sherry, Worcestershire and garlic. Cover. Cook on low 6-8 hours. Place French bread on a baking sheet. Sprinkle with cheese. Place under preheated broiler until lightly toasted. To serve, ladle soup into bowls. Float a slice of toasted French bread on top.
Makes 4-6 servings