Slow cooker caramelized French onion soup is an easy, restaurant-level dish that will disappear as fast as you serve it. Use your crockpot to first caramelize the onions. Then, add soup ingredients right in for a finished dish that is a home run - every time!

looking down on a finished bowl of caramelized French onion soup

Anyone else out there hate the idea of cutting onions? My eyes are watering just thinking about it! To keep my eyes from getting completely out of control, I have started wearing a pair of fitted swim goggles when I cut onions. Not a pretty sight!

But, this simple slow cooker soup is sooo worth it! In fact, just being able to use my slow cooker to make caramelized onions is worth it. Because once the onions are cut, every other step in the slow cooker version of this soup requires minimal prep. And....oooh that (yummy) smell!

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caramelized onion soup ingredients with labels

There are really two distinct parts to this soup. Caramelizing the onion and making the soup. You can't make the soup without the onions, BUT - you can make the onions without the soup. So this is really two amazing recipes in one.

To make the best slow cooker caramelized onions you will need:

Sweet onions - sliced
Olive oil

To make delicious French onion soup, you will also need:

Beef broth
Minced garlic
Cooking sherry
Worcestershire sauce
Dried thyme
French bread - sliced and toasted baguette
Gruyere cheese - mozzarella or swiss work too

🥣How to caramelize onions in a slow cooker

Caramelizing onions by using your slow cooker is life-changing. You no longer have to deal with smoke and a spattering mess. Cut onions into quarters and then slice each quarter. Use your hands to gently unnest the onion pieces.

Add sliced, raw onions into your slow cooker along with the olive oil. Toss to coat. Place cover on slow cooker, turn to low and do something else for 12-14 hours! I love doing this step in the evening and allowing my onions to cook overnight.

If you are not making soup, but just want unbelievably delicious and easy caramelized onions, stop here. These cooked onions are incredible on so many different dishes! Whether serving with cheesesteak sandwiches, chicken cheesesteaks, or on top of a good, lazy steak, they are truly next level. The key is just letting them cook on low heat for a long time!

a slow cooker full of caramelized onions

IMPORTANT NOTE: you can caramelize the onions on a cooktop in a more traditional format, if you prefer. But, regardless of how you do it, you must caramelize the onions before making the soup.

🍲Assembling Soup

From here, this French onion soup recipe just gets easier. Add all remaining ingredients, except for the French bread and cheese, into your crock pot and let it do it's thing. Cooking this delicious recipe on the low setting for several hours will bring out an amazing depth of flavor.

cooked onions on a spoon with soup in the backround

To serve your slow-cooker French onion soup, ladle soup into individual, ovenproof bowls. Place toasted French baguette slices (or other toasted crusty bread) into each bowl. Next, place a few slices of cheese on the top of the soup (bread) in each bowl.

Place oven-safe bowls on a baking sheet or rack under the broiler for about 5 minutes. Your soup is ready when the cheese becomes bubbly and starts to brown. Serve promptly!

a bowl of crockpot onion soup under the broiler

Storing leftovers

This is one of my favorite slow cooker soups! Not only is it delicious, but this hearty soup also freezes really well. Store your classic French onion soup in an airtight container.

Bread and cheese should be added fresh at the time of serving, not stored with the soup. This simple soup will stay fresh in the refrigerator for about 3 days and in the freezer for several months.

melted cheese on top of a bowl full of onion soup

↔️Substitutions

I generally feel that sweet yellow onions are the best onions for this recipe. Red onions and white onions would work as well.
If you are not a fan of gruyere cheese, you can substitute with slices of parmesan cheese or provolone cheese
Too lazy to toast your own French bread? Toast-like crackers will work for this cheesy toast topping
To make a vegetarian version of this soup, you can use a mushroom or onion broth rather than beef. Be sure to also swap the Worcestershire sauce with a vegetarian version.

a red crock full of onion soup top with melted cheese

😉Hints and hacks

If you plan to use these onions as a condiment rather than in soup, you may want to cook them with the lid off for that last hour or so. This will allow some of the excess liquid to evaporate.
Due to the long cooking time of the onions, it is a great idea to allow them to caramelize overnight. You can assemble the soup ingredients the next day.
This is an easy recipe to make using a slow cooker liner. This will allow for minimal clean-up.
To keep this slow cooker caramelized French onion soup more in line with healthy eating, you can skip the bread and cheese.
In the market for a new slow cooker? Here is my favorite!

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