Crockpot French Onion Soup

Ingredients

• 2 tablespoons butter, cubed
• 2 large sweet onions, halved and thinly sliced
• 1 large red onion, halved and thinly sliced
• 1/2 teaspoon coarsely ground pepper
• 2 cans (10-1/2 ounces each) condensed beef broth, undiluted
• 3 cups water
• 3/4 cup white wine or regular-strength beef broth
• 2 fresh thyme sprigs
• 1 fresh parsley sprig, optional
• 1 bay leaf
• 2 teaspoons Worcestershire sauce
• 16 slices French bread (1/4 inch thick)
• 3/4 cup shredded Gruyere or Swiss cheese