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overhead shot of french onion soup with thyme sprigs on top of gruyere toast
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Slow Cooker French Onion Soup

Slow Cooker French Onion Soup is everything you dream of in a French onion soup.  The slow cooker will slowly caramelize the onions to perfection.  Just add broth and fresh herbs and continue to slow cook.  The onions will melt in your mouth and of course, topped with baguette and oozy French Gruyere cheese.

Course Appetizer, Dinner
Cuisine American, French
Keyword Crockpot French Onion Soup, French Onion Soup, Onion Soup, Slow Cooker French Onion Soup
Prep Time 15 minutes
Cook Time 12 hours
Servings 8 Servings
Calories 366 kcal
Author Janet Barton


  • 3-4 large sweet onions organic, cut in half and sliced 1/8-1/4 inch thick
  • 1/2 cup unsalted butter
  • 1-2 tablespoons coconut sugar depending how sweet onions are
  • 1/2 teaspoon salt
  • 3 cloves garlic minced
  • 4 cups chicken bone broth
  • 4 cups beef bone broth
  • 1-2 tablespoons Worcestershire sauce
  • fresh thyme
  • 1 bay leaf
  • salt
  • fresh ground white pepper
  • fresh parsley
  • 1 loaf French Baguette Slice into 1-inch thick slices
  • 2-3 cups Gruyere cheese Shredded


  1. In the bowl of a crockpot melt butter. Add sliced onions, coconut sugar, 1/2 tsp. salt. Stir to coat onions. Add minced onions to the top of the onions.
  2. Cook on low for 4-5 hours. Stirring every 30 minutes or so.

  3. Add broths, about 4 sprigs of fresh thyme and 1 bay leaf.

  4. Cover and continue to cook on low for an additional 8 hours.
  5. Before serving add Worcestershire sauce to taste. Season with salt and white pepper and additional fresh herbs.
  6. Slice baguette into 1-inch slices. Butter both sides and place on a hot griddle or skillet until golden brown.

  7. Pour steaming hot soup into serving bowls. Top with 1-2 slices of baguette (enough to cover the top of the soup). Divide shredded gruyere cheese over the top of the baguette. Place under a broiler until cheese begins to bubble and is completely melted. Serve.

Recipe Notes

  • Soup can cook for as long as 12 hours on low. 
  • Can use 8 cups vegetable stock in place of Chicken and Beef broth.  
  • I like to cook the onions during the day, then add the broth and cook through the night.
  • Soup can be cooled and refrigerated for 3-4 days. Reheat when ready to serve.
  • This recipe can serve up to 8 depending on the size of bowls and amounts used per serving.
Nutrition Facts
Slow Cooker French Onion Soup
Amount Per Serving
Calories 366 Calories from Fat 216
% Daily Value*
Fat 24g37%
Saturated Fat 14g70%
Trans Fat 1g
Polyunsaturated Fat 2g
Monounsaturated Fat 7g
Cholesterol 67mg22%
Sodium 553mg23%
Potassium 188mg5%
Carbohydrates 19g6%
Fiber 1g4%
Sugar 2g2%
Protein 19g38%
Vitamin A 670IU13%
Vitamin C 1mg1%
Calcium 371mg37%
Iron 1mg6%
* Percent Daily Values are based on a 2000 calorie diet.