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Slow Cooker French Onion Soup

This hearty and delicious slow cooker French onion soup is a classic soup you can make in your Crockpot. The onions are caramelized beautifully, and give the soup a unique flavor.
Prep Time5 mins
Cook Time20 hrs
Course: Dinner, Soup
Cuisine: French
Keyword: crockpot, egg free, gluten free, nut free, onion soup, slow cooker, soy free
Servings: 4
Calories: 117kcal
Author: Tonje
Cost: Cheap




  • Peel the onions and slice them thinly. Add them to the slow cooker along with the butter. Place the lid on top, and leave the slow cooker on low for 10-12 hours, or overnight. The onions will caramelize and soften.
  • Then, add the stock and bay leaves. Leave the soup to cook for another 7-10 hours.
  • Remove the bay leaves and add salt and pepper to taste.
  • Add the soup to oven safe bowls. Place a thin slice of bread or a baguette on top, of the soup, and add cheese. Broil the soup in an oven until the cheese has melted. Serve immediately.


Do I have to add any liquid to the onions? – No. The onions will release moisture as they slow cook, and no liquid is required during the caramelization process.
Is this recipe allergy friendly? – Always consult the nutrition label of the ingredients you use. This recipe is generally egg free, nut free, gluten free and soy free.
Do you need to add seasoning to onion soup? – This soup has so much flavor from the caramelized onions. Some recipes use herbs or spices like thyme and cumin, but this is strictly not necessary. If you wish, you can experiement with adding additional seasoning.
Can I make French onion soup without the bread? – Of course! If you don’t want to use cheesy bread, you can serve the soup immediately straight from the Crockpot.
Which cheese should you use in French onion soup? - Gruyere is the traditional choice, but you can really use any cheese that you like.


Leftover slow cooker french onion soup can be stored in the fridge for up to 3 days, or frozen for up to 6 months. This recipe is perfect as a freezer meal for future dinners.
If you have leftovers, I highly recommend storing the soup without the cheesy bread on top. Otherwise, the bread will get soggy and might dissolve into the soup.

Top tips

My top advice for how to make the BEST french onion soup:
  • The longer the onions cook, the better they are. This is definitely a recipe you don’t want to rush.
  • French onion soup is typically enjoyed as a broth style soup with whole slices of caramelized onions. If you’re not too keen on the consistency of soft onions in soup, you can simply use a hand blender to puree the soup smooth.


Calories: 117kcal | Carbohydrates: 27g | Protein: 3g | Fat: 1g | Saturated Fat: 1g | Cholesterol: 1mg | Sodium: 1018mg | Potassium: 375mg | Fiber: 4g | Sugar: 13g | Vitamin A: 533IU | Vitamin C: 19mg | Calcium: 66mg | Iron: 1mg