Slow Cooker: French Onion Soup

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This Slow Cooker French Onion Soup is so much easier to make than traditional onion soup and tastes amazing! Made right in the crockpot.


This Crockpot French Onion soup is easy to make, packed with flavor, and surprisngly light and healthy. It's delicious on its own or topped with toasted bread and cheese.

It’s funny how you forget about food you really love sometimes. It sneaks off into some far expanse of your brain and until you see it (or in this case smell it) you had forgotten about it entirely. This is what happened to me with French Onion soup until a few days ago.

I was out for lunch with a friend and we had just ordered our own food when the irresistible aroma hit me. I turned toward it to find that all four people at the table next to us were just diving into their French Onion soups. There it was, flooding my nostrils with its deep and rich onion flavor, crunchy bread, and melty cheese. I had to turn away quickly before they all noticed me wiping drool of my chin. Yum.

Although I wanted it right then and there, we had just ordered and I hate being that person that changes her order around. So, instead of fulfilling my wish for the soup immediately, I settled for the following day by creating this delicious crockpot version that’s perfect for a cold night.

Crockpot French Onion soup in a red bowl with slices of toast.

What Is the Traditional Cheese for French Onion Soup?

Traditionally, this soup is served in a cup, ramekin, or soup bowl (or a mini cast-iron Dutch oven would be fun too) with a big slice of French bread on top (to serve as a giant crouton). The bread is then covered in aged gruyere and broiled until it's nice and toasty and bubbly.

If you don't have gruyere, don't worry. Swiss cheese is perfectly suitable as a substitute and it's what I always tend to use. Other cheeses you could use include provolone, parmesan, jarlsberg, beaufort, or comte.

How to make French Onion Soup from scratch?

The key to making French onion soup from scratch is cooking down the onions until they get browned, caramelized, and super soft. This is what gives the soup its deep and rich onion flavor. So whether you are making it in a slow cooker, stovetop, or Instant Pot - you always need to caramelize the onions. This is where the flavor comes from.

Once you have done that, the rest is easy. You just need broth, traditionally beef broth is used, some herbs like thyme, and then actual time. Cooking the soup for a long time is another key for French Onion soup, it develops the flavors.

What Makes This Slow Cooker French Onion Soup Healthy?

Don't let the bread and cheese fool you — this soup isn't as caloric as you might think. In fact, one cup (without the bread and cheese) has only 55 calories, 2 grams of fat, 8 grams of carbs, 3 grams of sugar, and nearly 4 grams of protein. In addition:

  • Onions are a great source of antioxidants and they also contain folic acid, fiber, and vitamin B which is responsible for healthy new cell creation.
  • Butter (just a little) provides fat that your body needs to keep your systems running smoothly and is also used as brain food.
  • Worcestershire sauce and balsamic vinegar are similar in their nutritive properties, in that they both help with digestion, blood circulation, enhanced immunity effects, and have both been noted to improve digestion, nervous system function, and fight against free radicals.
  • Garlic is known for its immune system-boosting properties. It also is used as an antifungal and antiviral and also has antioxidant properties. It's also heralded as a heart helper and can lower your cholesterol.
  • Spices such as salt, pepper, and thyme add flavor and inflammation-boosting properties without adding calories or fat.
  • Vegetable broth (or chicken or beef) is known to help your hair, nails, and skin remain healthy and vibrant. Animal broths are also good for your muscles, connective tissues, and joints.

French Onion soup in a red bowl with melted cheese and toast.

Side Dishes to Serve With Crockpot French Onion Soup

If you ask me, no soup is complete without a side salad or sandwich. (It makes me feel more like I'm eating at a restaurant this way.) To that end, some things I'd serve with this soup include:

  • This Grilled Eggplant Sandwich that also has a black olive spread on it that is to die for. This keeps with a vegetarian-themed meal if you prefer and is chock full of so many veggies and good things, you'll wonder why you haven't paired these two dishes together before.
  • A simple side salad works well here too, get a nice spring mix and add in shredded carrots, thinly sliced bell peppers, some cucumbers and cherry tomatoes, sliced in half longways. Add feta or goat cheese crumbles or some slivered almonds and your favorite light dressing.
  • Use leftover chicken in a pita and stuffed with your favorite toppings and condiments as a nice complement to the French Onion Soup. Serve it hot or cold.
  • This Israeli Chopped Salad is a family favorite and can be made a day or two in advance and brought back out and served with just about anything you can think of — including piping hot soup!
  • Chickpea, Avocado, and Feta Salad is another one that's easy to put on repeat and eat, eat, eat.
  • If you want the soup to be your main focus, you can also serve a mini charcuterie board on the side with some more thinly sliced bread and an assortment of cheeses, fruit, and pickled veggies.

This post was originally shared in 2012 but has been updated with new photos, tips, and ideas.

The Recipe
Slow Cooker French Onion soup in a bowl with bread and melted cheese.

Slow Cooker: French Onion Soup

COOK TIME: 8 Hours
TOTAL TIME: 8 Hours, 15 Min
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  • 4 sweet onions, sliced
  • 2 tbsp butter
  • 1 tbsp Worcestershire sauce
  • 1 tbsp balsamic vinegar
  • 3 garlic cloves, minced
  • 2 tsp brown sugar (or Stevia)
  • 1/2 tsp pepper
  • 1/2 tsp salt
  • 3 tbsp all-purpose flour
  • 64 oz vegetable broth (or chicken broth or beef broth)
  • 2 tbsp fresh thyme

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Set your crockpot to high and add the onions, butter, Worcestershire sauce, vinegar, garlic, brown sugar, salt, and pepper. Cook for 60 minutes until onions begin to brown and caramelize, stirring occasionally.


Stir in the flour and let cook for 5 more minutes.


Add the broth and thyme. Cook on low for 6-8 hours.


To serve with bread and cheese, slice a small piece of french bread and place on top of the soup. Cover with one slice of Swiss cheese and broil for 3 minutes.

Nutritional Facts
Serving Size: 1 cup (303g)
Amount Per Serving
Calories 111
Calories from Fat 28
% Daily Value *
Total Fat 3g
Saturated Fat 2g
Monounsaturated Fat 0g
Polyunsaturated Fat 0g
Cholesterol 8mg
Sodium 1090mg
Total Carbohydrate 20g
Dietary Fiber 2g
Sugars 12g
Protein 2g

* Percent Daily Values are based on a 2,000 calorie diet. Your daily values may be higher or lower depending on your calorie needs.

The Nutritional Values provided are estimates only and may vary based on the preparation method.


Add French bread and reduced fat Swiss cheese for a true French Onion soup experience.
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About the authorMeet Kristen McCaffrey
Hi, I’m the cookbook author, recipe developer, and food enthusiast behind Slender Kitchen. I am obsessed with making healthy food that is easy to prepare and absolutely delicious. Meal planning is my secret weapon and I hope I can make meal time easier for you with our tried and tested recipes and foolproof meal plans. Learn More
On Slow Cooker: French Onion Soup
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December 5, 2019 - 13:10
is the 3 points include the french bread slice and swiss cheese?
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February 12, 2019 - 11:08
Do the 3 points include the bread and cheese? Or do the three points just cover the soup?
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January 9, 2019 - 09:22
Do you have this recipe for the instant pot?
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January 9, 2019 - 15:58
I haven't tried it in the Instant Pot yet. But here is what I would do if you want to try it. Add the onions, butter, Worcestershire sauce, vinegar, garlic, brown sugar, salt, and pepper to the Instant Pot on the saute function. Cook for about 5 minutes until they begin to soften. Then add about 1/4 cup of broth and cover the Instant Pot. Cook on Manual mode for 20 minutes. This should result in some caramelization and flavor from the onions. Open and add the remaining ingredients. Then close with cook for 10 minutes.
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Marlo Cooley
October 28, 2015 - 15:46
Add a Rating:
This recipe is exactly how it was described and so satisfying for an amazing bowl of French Onion Soup! I will make this again and again!
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