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Close-up of a crock of French onion soup topped with a piece of toasted baguette and rich, golden-brown melted Gruyère cheese, garnished with fresh thyme.

Crockpot French Onion Soup

This Crockpot French Onion Soup is rich, deeply caramelized, and full of savory flavor. Slow-cooked onions in a hearty beef broth make this classic French dish effortless yet restaurant-worthy.
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Prep Time 15 minutes
Cook Time 8 hours
Total Time 8 hours 15 minutes
Servings: 6 bowls
Course: Soup
Cuisine: French
Calories: 370
Ingredients Equipment Method Notes

Ingredients
  

Soup Base
  • 4 large yellow onions thinly sliced
  • 3 tbsp unsalted butter
  • 1 tbsp olive oil
  • 2 cloves garlic minced
  • 1 tsp sugar helps caramelize onions
  • 1 tsp salt
Broth and Flavoring
  • 6 cups beef broth low-sodium preferred
  • 1/2 cup dry white wine optional
  • 1 tsp Worcestershire sauce
  • 1 bay leaf
  • 1 tsp fresh thyme leaves or 1/2 tsp dried thyme
For Serving
  • 6 slices French baguette toasted
  • 1 1/2 cups grated Gruyère cheese or Swiss cheese

Equipment

  • Crockpot or slow cooker
  • Oven-safe soup bowls
  • Cheese grater

Method
 

  1. Add sliced onions, butter, olive oil, garlic, sugar, and salt to the Crockpot. Stir to coat the onions evenly.
  2. Cover and cook on LOW for 8 hours or until onions are deep golden and caramelized.
  3. Add beef broth, wine, Worcestershire sauce, bay leaf, and thyme. Stir and cook on HIGH for 1 additional hour.
  4. Remove the bay leaf and taste the soup. Adjust seasoning with salt if needed.
  5. Ladle soup into oven-safe bowls, top each with a toasted baguette slice, and sprinkle generously with grated Gruyère cheese.
  6. Broil the bowls in the oven until the cheese is melted and bubbly, about 2–3 minutes. Serve immediately.

Notes

For even richer flavor, you can caramelize the onions in a skillet before adding them to the Crockpot. Gruyère is traditional, but mozzarella or Swiss cheese works well too.