French Onion Soup - Slow Cooker (Crock Pot)

Ingredients

• 4 Tbsp. Light butter
• 6 thyme sprigs
• 1 bay leaf
• 5 pounds large sweet onions, vertically sliced (about 16 cups)
• 1 tablespoon sugar
• 3 cups unsalted beef cooking stock
• 3 cups 50% less sodium beef broth
• 2 tablespoons red wine vinegar
• 1 teaspoon kosher salt
• 1 teaspoon black pepper
• 12 (1-ounce) slices whole grain French bread baguette
• 5 ounces Gruyere cheese, shredded (about 1 1/4 cups)