Ingredients:

  • 5 lbs yellow onions, thinly sliced
  • 4 tbsp unsalted butter
  • 1 tsp salt
  • 6 cups beef broth
  • 1 cup dry white wine
  • 2 cloves garlic, minced
  • 1 bay leaf
  • 1 tsp dried thyme
  • 1 tbsp Worcestershire sauce
  • ½ tsp black pepper
  • 1 French baguette, sliced into 1-inch rounds
  • 2 cups Gruyère cheese, shredded
  • 1 cup Mozzarella cheese, shredded

Instructions:

  1. Melt the butter in a large skillet over medium-high heat. Add the sliced onions and salt, stirring occasionally for 15–20 minutes until the onions are deeply golden and caramelized.
  2. Transfer the browned onions to the slow cooker. Stir in the minced garlic, dried thyme, and Worcestershire sauce.
  3. Pour in the beef broth and dry white wine, then nestle the bay leaf on top.
  4. Cover and cook on Low for 8 hours or High for 4 hours until the broth has darkened and the onions are completely tender.
  5. During the final 30 minutes of cooking, toast the baguette slices in the oven until crisp.
  6. Ladle the hot soup into oven-safe ramekins. Top each bowl with a toasted bread slice and a generous blend of shredded Gruyère and Mozzarella cheese.
  7. Place the ramekins under the broiler for 2–3 minutes until the cheese is melted and bubbling.