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Home » Soups » Slow Cooker French Onion Soup

Slow Cooker French Onion Soup

by Sarah Olson on December 19, 2020 | Updated December 31, 2020 2 Comments

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close up of french onion soup on wooden spon
collage of french onion soup images with text overlay for pinterest

Make Slow Cooker French Onion Soup in your slow cooker. It has a rich buttery onion broth that is great with homemade croutons and cheese broiled on top.

It’s soup season (actually, every season is soup season for me). My family also enjoys baked potato soup and ham and bean soup.

close up of french onion soup on wooden spon

Here is my version of French Onion Soup in the slow cooker. My version doesn’t just taste like beef broth and onions. I add butter, balsamic vinegar, and spices, so the soup has a depth of flavor and see my tips for making the croutons that go under the cheese when serving.

What do I need to make French Onion Soup:

  • Onions – Use sweet yellow onions (white or yellow work too)
  • Sugar – Optional, only use if you can’t find sweet yellow onions
  • Salted Butter – Used to caramelize the onions
  • Flour – Added to the butter and onions. This will add some body to the soup.
  • Beef broth – Can use chicken if desired.
  • Balsamic Vinegar – Adds flavor and touch of tang.
  • Worcestershire sauce – My secret ingredient.
  • Seasonings – Salt, pepper, oregano, thyme, garlic, and a bay leaf.
  • Toppings – Homemade Croutons (recipe below), swiss cheese, and parmesan cheese.
ingredients for french onion soup in front of a slow cooker

How to carmelize the onions:

  • Set a pan to medium-high heat. Add the butter. When the butter is melted, add the onions and sprinkle with salt and pepper.
  • Cook the sliced onions until browned and caramelized; this can take 10 or more minutes. Stir often.
  • I add the flour to the butter and onions and cook for 2 more minutes.
2 photo collage. One photo is a bowl of sliced onions. Other photo caramelized onions in skillet.
  • Add remaining ingredients.
  • Stir.

How long do I cook?

  • Place the lid on the slow cooker.
  • Cook on HIGH for 4 hours or on low for 8 hours.
french onion soup in slow cooker

How to make homemade croutons for French Onion Soup:

  • Preheat the oven to 500 degrees (broil).
  • Cut a baguette into 1/4 inch slices. Place slices on a sheet pan.
  • Using a pastry brush, brush olive oil onto the slices.
  • Place the sheet pan under the broiler. Cook for about 3-5 minutes or until browned and toasty.
  • Cut a garlic clove tip off and rub each piece of cooked bread with it. This will give the bread garlic flavor.

What can I use instead of bread for French Onion Soup?

  • Store-bought croutons – Yes! This works well. When I worked at Marie Callender’s, they used bagged croutons for their French Onion Soup.
  • Garlic bread – Cut a loaf of store-bought garlic bread into cubes. Broil until crisp and browned.
  • Stove-top stuffing – This buttery onion soup is amazing topped with a bit of stuffing mix under the cheese.
sliced bread that is toasted on tray

How to assemble French Onion Soup:

  1. Fill an ovenproof bowl with the French Onion Soup broth. Place the bowl in a pie tin or on a sheet pan. (You can make more than one bowl at a time).
  2. Add the homemade croutons (or store-bought) on top of the soup.
  3. Place 1-2 swiss cheese pieces (can use provolone or gruyere) and sprinkle on parmesan cheese.
  4. Broil until the cheese starts to brown and is bubbly.
4 photo collage about how to top french onion soup with croutons and cheese, then broil.

Can I freeze this soup?

  • Yes, you can freeze the leftover soup (without the croutons and cheese).
  • Place the cooled soup into freezer ziplock bags or freezer containtes.
  • Freezer for up to 3 months.
  • Thaw in fridge for 24 hours before needing.
  • Reheat on the stove-top or microwave.
french onion soup with spoon in it.

Try one of these soups next:

  • Slow Cooker Stuffed Pepper Soup
  • Slow Cooker Broccoli Cheese Soup
  • Slow Cooker Turkey Chowder
  • Slow Cooker Black Bean Soup
  • Slow Cooker Chicken Noodle Soup

Want to make more magic in your crockpot? Stay up to date and subscribe to my newsletter and follow along on Facebook, Instagram, Pinterest and YouTube.

close up of french onion soup on wooden spon

Slow Cooker French Onion Soup

5 from 7 votes
Rich and decadent French Onion Soup made in a slow cooker. Top with homemade croutons and cheese, then broil.
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Course: Soup
Cuisine: American
Keyword: French Onion Soup
Prep Time: 25 minutes
Cook Time: 4 hours
Total Time: 4 hours 20 minutes
Servings: 10
Calories: 132kcal
Author: Sarah Olson

Equipment Needed:

  • Slow Cooker – 5 quart or larger

Ingredients:

  • 1 stick butter
  • 5 sweet yellow onions sliced
  • 1 tsp. salt
  • 1/4 tsp. pepper
  • 1/4 cup flour
  • 64 oz. beef broth (two 32-oz. containers)
  • 1 tsp. sugar (optional) I only use this if my onions aren't labeled "sweet onions"
  • 2 tsp. minced garlic
  • 1/4 tsp. dried thyme (not ground)
  • 1/4 tsp. dried oregano (not ground)
  • 1 tsp. Worcestershire sauce
  • 1 Tbsp. balsamic vinegar
  • 1 bay leaf

For serving (not included in nutritional count)

  • 1 baguette
  • olive oil
  • 1 whole garlic clove
  • sliced swiss cheese (can use provolone or gruyere) (about 2 slices needed per serving)
  • shredded parmesan cheese (use about 1 tablespoon per serving)

Instructions:

  • In a large skillet set to medium high heat, add the butter. When the butter is melted add the sliced onions. Sprinkle with the salt and pepper.
  • Saute the onion until browned and caramelized. This will take about 10 minutes. Stir often. Adjust the heat if they start to burn.
  • When the onions are done cooking add the flour to the butter and onions. Cook for 2 more minutes.
  • Add the floured onions to the slow cooker. Add the beef broth, sugar (if using), garlic, thyme, oregano, Worcestershire sauce, and balsamic vinegar. Stir well. Add the bay leaf on top.
  • Cook on HIGH for 4 hours or LOW for 8 hours.
  • Remove bay leaf before serving.

How to make the homemade croutons:

  • Preheat the oven to 500 degrees (broil).
  • Cut a baguette into 1/4 inch slices. Place slices on a sheet pan.
  • Using a pastry brush, brush olive oil onto the slices.
  • Place the sheet pan under the broiler. Cook for about 3-5 minutes or until browned and toasty.
  • Cut a garlic clove tip off and rub each piece of cooked bread with it. This will give the bread garlic flavor.

How to assemble the bowls of soup:

  • Fill an ovenproof bowl with the French Onion Soup broth. Place the bowl in a pie tin or on a sheet pan. (You can make more than one bowl at a time).
  • Add the homemade croutons (or store-bought) on top of the soup.
  • Place 1-2 pieces of swiss cheese (can use provolone or gruyere) and sprinkle on parmesan cheese.
  • Broil until the cheese starts to brown and is bubbly.

How to Video:

Recipe Notes:

What can I use instead of bread for topping this soup?
  • Store-bought croutons – Yes! This works well. When I worked at Marie Callender’s, they used bagged croutons for their French Onion Soup.
  • Garlic bread – Cut a loaf of store-bought garlic bread into cubes. Broil until crisp and browned.
  • Stove-top stuffing – This buttery onion soup is amazing topped with a bit of stuffing mix under the cheese.
Can I freeze the leftover soup?
  • Yes, you can freeze the leftover soup (without the croutons and cheese).
  • Place the cooled soup into freezer ziplock bags or freezer containtes.
  • Freezer for up to 3 months.
  • Thaw in fridge for 24 hours before needing.
  • Reheat on the stove-top or microwave.
Nutritional values do not include croutons or cheese (every bowl size will need different amounts of cheese and croutons, that is why I can not add this value).

Nutrition:

Calories: 132kcal | Carbohydrates: 9g | Protein: 3g | Fat: 10g | Saturated Fat: 6g | Cholesterol: 24mg | Sodium: 954mg | Potassium: 186mg | Fiber: 1g | Sugar: 3g | Vitamin A: 282IU | Vitamin C: 4mg | Calcium: 28mg | Iron: 1mg
Made this recipe?I want to see your photos! Tag me on Instagram @themagicalslowcooker
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    Filed Under: Soups Tagged With: cheese, crockpot, french onion, onion, slow cooker, soup

    Comments

    1. Alicia says

      February 8, 2021 at 8:25 am

      Can I use Vegetable Broth

      Reply
      • Sarah Olson says

        February 8, 2021 at 8:33 am

        yes

        Reply

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