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Slow Cooker French Onion Soup

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Slow cooker French onion soup is the most delicious way to enjoy this bistro classic while hitting the easy button at the same time! Simply caramelize the onions overnight, let the soup cook all day in the slow cooker, and come home to mouthwatering results.

three bowls with soup covered in broiled cheese

Just going to hang out over here, living my best soup lady life. It’s just so good, especially this rich, savory, toasty bread and gooey cheese french onion soup that is absolutely ridiculously easy to make.

Here are the major loves going on in each bowl of comfort:

  • slow-cooked caramelized onions that require little effort
  • sweet, mellow onions
  • rich beef broth
  • balance of savory and sweet flavors
  • hearty bread 
  • gooey, tangy Gruyere cheese

close up of broiled cheese and toast with fresh tyme sprig on a bowl of soup

Normally French onion anything can elicit a sigh of “ok, it’s going to take a while but it’ll be worth it.” Except for this time we’re calling in the slow cooker for reinforcements and everything practically makes itself!

True caramelized onions are a labor of love, cooked slowly over low heat in equal parts butter and oil with a generous sprinkle of salt. They’re a great addition to so many meals like pizza, pull-apart bread, and of course soul comforting soup.

french onion soup in the slow cooker with ingredients

WHAT ONIONS SHOULD YOU USE?

Sweet onions are traditional and mild. They hold a good texture even after the long caramelization process. Sweet onions are recommended, but red onions and yellow onions can be used as well. Red onions will add a more robust flavor and less sweetness.

Yellow onions will be sweeter than reds with more onion flavor and are a great substitute if you can’t find sweet onions.

HOW TO MAKE SLOW COOKER FRENCH ONION SOUP

Mild prep. Set it and forget it.

Seriously, the effort involved is so low you’re going to want to make this soup again and again.  There’s two ways you’re going to want to set up the timing to make this soup.

  1.  Prep the onions at night.  Set in the slow cooker with butter, oil, and salt.  Cook on low overnight.  In the morning make the soup and cook on low all day – about 8 to 10 hours.
  2. Prep the onions in the morning.  Cook on low all day.  Make the soup and cook on high for 4 to 6 hours.

Once the soup is done, you just need to add the finishing touches of hearty bread and melty cheese!

collage of process shots for plating french onion soup

Laddle the french onion soup into oven safe bowls.  Most ceramic bowls are oven safe, but you can check the bottle of the bowl where it will usually confirm that.  Bowls or soup crocks with handles are the best option since the bowl will be super hot after broiling.  You’re definitely going to want oven mits to take out of the oven, even if placed on a baking sheet.

What goes on top of french onion soup

Bread and cheese!  I mean, what’s better with soup than bread and cheese?!

For bread, I like to use sourdough or crusty soup bread, sliced so one or two slices fit in the bowl.  It’s okay if they stick out too.  You can toast them if you don’t want them too soggy, but also using a heartier bread like sourdough, baguette, or ciabatta will keep it from falling apart.

layering sliced of sourdough on top of soup

Gruyere is the traditional cheese used for French onion soup.  It’s a hard, mild, and tangy cheese.  If you can’t find Gruyere, Swiss cheese is a great substitute.  

Layer the shredded cheese on top of the bread.  Then broil in the oven on high until the cheese is melted and browning.  

Tip: Place the bowl on a sheet tray before place under the broiler.  This will make transferring in and out of the oven easier and if any of the melted cheese drips it won’t make a mess of your oven!

Enjoy your hot soup right away!  If you’re making this in advance, wait to add the toast and cheese and do that part right before you serve.  Whether it’s making it in advance or sneaking a homemade meal in while multitasking, you’re going to love the rich, fancy taste of slow cooker french onion soup without having to do any work!

Did you make this recipe?  Please leave a rating and comment below and don’t forget to add a photo of your eats with the pins on Pinterest!

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close up of broiled cheese and toast with fresh tyme sprig on a bowl of soup

Slow Cooker French Onion Soup


  • Author: Lauren
  • Prep Time: 10 minutes
  • Cook Time: 18 hours
  • Total Time: 18 hours 10 minutes
  • Yield: 8 servings 1x

Description

Bistro-style French Onion Soup made easy in the slow cooker!  You’ll love how simple it is to make while you spoon up bites of sweet and savory onion, rich beef broth, hearty bread and gooey melted cheese.


Ingredients

Scale
  • 3 pounds sweet onions, sliced in half-moons
  • 2 tablespoons unsalted butter, melted
  • 2 tablespoons olive oil
  • 1/2 teaspoon salt
  • 1/4 cup brandy
  • 8 cups beef broth
  • 4 sprigs of thyme
  • 2 bay leaves
  • 1/2 teaspoon chopped garlic
  • salt and pepper, to taste
  • 1 loaf sourdough bread, or another hearty bread like baguette or ciabatta
  • 1/2 pound Gruyere or Swiss cheese, fresh grated

Instructions

  1. Caramelize the onions. Slice the onions into thin half-moon slices. In the slow cooker, combine the onions, butter, olive oil, and salt. Cook on low for 10 to 12 hours.
  2. Make the soup. Once the onions have cooked down, add the brandy, beef broth fresh thyme, bay leaves, and garlic.
  3. Cook the soup. Cook on low for 8 hours or high for 4 hours. Season with salt and black pepper to taste.
  4. Toast and broil. Just before the soup is done cooking, slice the bread into 2 to 4 inch wide slices, and grate the cheese. Toast the bread until golden brown. Ladle the soup into oven-safe bowls, top with toast and grated cheese. Set all the bowls on a sheet tray and broil on high for 3 to 5 minutes until the cheese is melted and starting to brown. Serve immediately.

Notes

  • Onions can be caramelized in advance and then used to make the soup when you’re ready.
  • There two options for timing to cook the soup.  Option 1: Cook the onions overnight for 10 to 12 hours.  In the morning, add the soup ingredients and cook on low for 8 hours or high for 4 hours.  Option 2:  Set the onions to cook in the morning all day, then make the soup and high cook for 4 hours for dinner.
  • Category: Soup
  • Method: Slow Cooker
  • Cuisine: French

Keywords: french onion soup, slow cooker french onion soup, crock pot french onion soup

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