Skip to Content

Slow Cooker French Onion Soup

Slow Cooker French Onion Soup is so easy and super delicious. Lots of deep flavor from the caramelized onions.

Slow Cooker French Onion Soup is one of the easiest soups I’ve ever made. It’s very much a set it and forget it recipe. 

Is French Onion Soup bad for you?

This soup is actually very nutritious. Onions are a part of the allium family. Onions like other vegetables in the allium family has quercetin.  Quercetin is an antioxidant and an anti-inflammatory. According to it can reduce risks of heart disease, cancer, and degenerative brain disorders.

Onions also have allicin. Once an onion is cut it produces allicin. If you allow the onion to sit after cutting it for about 10 minutes before cooking it, you will get the most benefits from it. Allicin which is also found in garlic, may also lower blood sugar, cholesterol, and blood pressure. It also does what quercetin does. 

What kind of onions is best for French Onion Soup?

Sweet onions will have the best flavor when caramelized. However you can also use yellow or white onions. The only onions I wouldn’t use are red. They tend to be a little more bitter.

Yield: 10 servings

Slow Cooker French Onion Soup

Slow Cooker French Onion Soup

Slow Cooker French Onion Soup is so easy and super delicious. Lots of deep flavor from the caramelized onions.

Caramelizing the onions 12 hours
Cooking the Soup 8 hours
Additional Time 10 minutes
Total Time 20 hours 10 minutes


Caramelized Onions

  • 3 lbs sweet onions
  • 2 Tbsp olive oil
  • 2 Tbsp unsalted butter
  • 2 tsp salt
  • 1 tsp black pepper


  • 10 cups beef broth
  • 2 Tbsp balsamic vinegar

To Serve

  • 1 baguette
  • 2 cups shredded gruyere cheese


I normally start this the evening before I want to eat this soup.

Caramelizing the Onions

  1. Turn 6 quart slow cooker on to low.
  2. Slice onion in half and then slice with half moons. Allow to sit for 10 minutes to get the most health benefits.
  3. While you are waiting on the onions, add butter to slow cooker. Allow to melt.
  4. Add olive oil.
  5. Place onions in slow cooker.
  6. Sprinkle with salt and pepper. Using tongs mix the onions around to coat with butter and olive oil.
  7. Place the lid on the slow cooker and cook for 12 hours.

Cooking the Soup

  1. Add beef broth and balsamic vinegar. Mix gently.
  2. Set to cook on low for 6-8 hours. The longer the better.
  3. Dish soup into bowl. Top with slices of baguette and sprinkled with a generous amount of gruyere cheese. Place on sheet pan and place under broiler in oven.
  4. Enjoy.

Nutrition Information:



Serving Size:


Amount Per Serving: Calories: 301Total Fat: 15gSaturated Fat: 7gTrans Fat: 0gUnsaturated Fat: 7gCholesterol: 34mgSodium: 1745mgCarbohydrates: 28gFiber: 2gSugar: 9gProtein: 15g

The nutritional information provided here is not guaranteed to be accurate and is provided for informational (and google) purposes only.

Meet Kerry

Why not join us on Pinterest: Coffee With Us 3  or hangout with us on Facebook:  


Coffee With Us 3 will use the information you provide on this form to be in touch with you and to provide updates and marketing. Please let us know all the ways you would like to hear from us:

You can change your mind at any time by clicking the unsubscribe link in the footer of any email you receive from us, or by contacting us at We will treat your information with respect. For more information about our privacy practices please visit our website. By clicking below, you agree that we may process your information in accordance with these terms.

We use Mailchimp as our marketing platform. By clicking below to subscribe, you acknowledge that your information will be transferred to Mailchimp for processing. Learn more about Mailchimp’s privacy practices here.

Don’t forget to pin!

Skip to Recipe