Slow Cooker French Onion Soup

Let this healthy, soothing slow cooker French onion soup cook itself while you’re busy with other things. Make it with bone broth for a boost of collagen.

  • Author: Sharon Chen
  • Prep Time: 10 minutes
  • Cook Time: 20 hours 22 minutes
  • Total Time: 20 hours 32 minutes
  • Yield: 10 - 12 servings 1x
  • Category: Soup
  • Method: Slow Cooker
  • Cuisine: French


  • 3 pounds yellow onions, peeled and sliced
  • 2 tablespoons unsalted butter
  • 2 tablespoons olive oil
  • 1 teaspoon salt, plus more to taste
  • Freshly ground black pepper
  • 2 tablespoons balsamic vinegar
  • 10 cups beef bone broth or homemade beef bone broth or low sodium beef broth
  • 3 tablespoons Sherry, optional

For assembling the soup:

  • 6 baguette slices for each bowl
  • 1 1/3 to 2 cups grated or shaved Gruyere cheese
  • Chopped parsley for garnishing


  1. Place onions in a 6-quart slow cooker. Stir in butter and olive oil. Season with salt and pepper. Cover and cook on low for 12 hours.
  2. Add balsamic vinegar and beef bone broth into the slow cooker. Add Sherry if using.
  3. Cover and cook on low for another 6-8 hours.
  4. Preheat oven to 350°F.
  5. Portion and ladle the soup and onions into oven-safe bowls and place the bowls on a baking sheet.
  6. Top each bowl with a slice of toast and a generous amount of grated or shaved Gruyere cheese.
  7. Bake on a rack in the upper third of the oven for 20-30 minutes or until the cheese is melted.
  8. Switch oven to broil and broil the soup for 2-3 minutes until the cheese is browned.
  9. Garnish with chopped parsley and serve warm.


Recipe adapted from The Kitchn.


Keywords: slow cooker french onion soup