This slow-cooked French Onion Soup is rich, savory, and topped with gooey melted cheese and toasted bread. It's the perfect comfort food for chilly days, with minimal effort thanks to the Crockpot.
In a large skillet over medium heat, melt butter and olive oil. Add sliced onions, sugar, salt, and pepper. Cook, stirring occasionally, for 20–25 minutes, until golden and caramelized.
Transfer the caramelized onions to the slow cooker. Add minced garlic, Worcestershire sauce, dry white wine (if using), beef broth, thyme, and bay leaf. Stir to combine.
Cover and cook on low for 8–10 hours or on high for 4–5 hours until the soup is rich and flavorful.
Remove the bay leaf and adjust the seasoning to taste.
To serve, preheat the broiler. Place baguette slices on a baking sheet and toast for 1–2 minutes per side, until crisp.
Ladle the soup into oven-safe bowls. Top with toasted baguette slices and a generous amount of shredded cheese.
Place the bowls under the broiler for 2–3 minutes until the cheese is melted, bubbly, and golden.
Serve hot and enjoy your comforting Crockpot French Onion Soup!