Slow Cooker French Onion Soup is loaded with caramelized onions and Gruyere cheese. One bowl of this deliciously cheesy, onion-filled soup just isn’t going to be enough!

Slow cooker French onion soup in white bolw with spoon

We are huge fans of soups. Not only are they super simple to whip up in a jiffy, but they’re so hearty and full of flavor. We make them a lot during the winter months. There’s just nothing as good as a hot soup on a cold, blustery day to make you feel cozy.

We are always ready to start creating delicious homemade crockpot soups. Simply put, the only thing better than soup is easy to make soup.

This Slow Cooker French Onion Soup is a soup we make all year long. It’s hearty and warm in the winter, so good with fresh onions in the summer, and the flavor is something we can’t get enough of any time of year. We love french onion soup and could eat it almost any time. And it’s so easy, we CAN eat it almost any time.

Where did French Onion Soup Get its Name?

French onion soup actually originated in France in the 18th century and has been a traditional soup of France ever since. Leave it to the French right?

Two Theories on Origin

There are two theories, or myths, depending on who you ask, surrounding French onion soup. Both of them agree that the soup originated with King Louis XV.

The first story goes that after a long day of deer hunting, King Louis XV came back to his lodge to find that their larder was almost completely bare. All he and his great aunt could find were onions, butter, and champagne. AS necessity is the mother of invention, the story goes that King Louis and his aunt simply threw all of those ingredients into a pot and cooked them up. Thus French onion soup was born.

The second theory revolves around the Duke of Lorraine who stopped into La Pomme d’Or, a restaurant in the town of Chalons-en-Champagne, on his way to the Palace of Versailles where the Duke was to visit his daughter, Queen Marie, wife of Louis XV.

While there, the Duke had an onion soup created by the chef there and was so taken with it that he descended from his room to the kitchen, in his bathrobe, no less, to watch the cooks prepare the soup.

Slow Cooker French Onion Soup

To me, this French onion soup stands out because it’s honestly beyond simple to make – and I love the stories behind it. It’s literally as simple as adding in the ingredients, going about your business and running errands, and coming home to warm up by the fireplace with a nice hot bowl of soup.

While you’re out and about, don’t forget to pick up a loaf of french bread to go right along with this slow cooker soup!

Ingredients

You only need a few ingredients to make this super simple slow cooker French onion soup. In fact, the ingredient list is just as easy as the rest of the recipe.

To make this soup, you’ll need yellow onions, butter, olive oil, kosher salt, black pepper, beef broth, balsamic vinegar, and gruyere, mozzarella, or asiago cheese. Of course, you can mix them all if you like.

Making Slow Cooker French Onion Soup

Once you read how to make this slow cooker French onion soup, you’ll agree that it’s one of the easiest soup recipes you’ll ever make. It’s really quite simple.

Place the sliced onions in a 5 qt. or larger slow cooker.
Drizzle over the butter and olive oil.
Sprinkle the salt and pepper over the top and cook on LOW for 12 hours. (Do this overnight)
Add in the broth and balsamic vinegar.
Stir and cook on LOW for an additional 8 hours.
Preheat oven to 350F.
Arrange 4-6 oven safe bowls on a sturdy baking sheet.
Ladle the soup into the bowls.
Top with a slice of toasted french bread and 1/3 cup of cheese each. Add more cheese if you like.
Bake 20-25 minutes or until the cheese is browned to your liking.
Cool 2-3 minutes before serving.

PIN IT!!

Can You Substitute Chicken Broth for Beef Broth?

I’ve been asked this question several times. While I’m sure you technically can, it will change the overall taste and flavor of the soup. The beef broth gives a nice, hearty, and salty flavor that mixed so well with the onions. If you’re wanting to change out for another liquid base, do so but just know that it won’t taste quite the same.

In this recipe, the beef broth and onion have the time to meld together to develop a wonderful full body flavor. This of course can be done on the cooktop also but by using your slow cooker you can set it and forget it! On the cooktop, you would have to watch the onions, keep on stirring so they don’t burn. That is time-consuming. If I can use my slow cooker to make my life easier you can be sure I’m going to do it.

How to Serve Slow Cooker French Onion Soup

This soup is mostly served as a starter, but considering how good it is, we eat this as a meal. A nice big bowl of this hearty soup and some nice crusty bread and you have total deliciousness! Add a salad if you like but we skip it the soup is hearty enough for us.

Slow Cooker French Onion Soup Variations

For me, nothing beats slow cooker French onion soup served all by itself. But I do know that others like to add on some extra toppings. You could add a bit more cheese on top (because you can never have too much cheese, right?!) or even chop up some chives and sprinkle them on as well.

I’ve even known people to add in some fresh jalapenos to give it a bit of a kick!

Storing Slow Cooker French Onion Soup

You can store any slow cooker French onion soup leftovers you have in the refrigerator in an air-tight storage container for about 4 days.

For longer storage, you can freeze this soup in an air-tight, freezer-safe container or heavy-duty freezer bag for up to 3 months.

Slow Cooker French Onion Soup FAQ

Q: Can I substitute other broth for the beef broth?
A: You CAN do that, but be aware that it will change the flavor of your soup. Classic French onion soup uses beef broth.

Q: Can I put meat in this soup?
A: Yes, you can. Chicken cutlets or boneless pork both work well.

Q: How do I serve this slow cooker French onion soup?
A: This is a simple soup that’s best served simply. All you need is a bowl and a piece of crusty bread.

Q: How long does Fench onion soup keep?
A: You can store this soup in an air-tight container in the fridge for up to 4 days. You can freeze it for up to 3 months in an air-tight, freezer-safe container or heavy-duty freezer bag.

You Need Slow Cooker French Onion Soup in Your Life

You just didn’t know it. Don’t overlook the power of a delicious bowl of homemade french onion soup. Let your slow cooker take over and save you from spending hours in the kitchen cooking!

Don’t wait for the colder weather to get here. The time is now to get your soup planning ready and slow cooker French onion soup is the perfect soup recipe to start!

Slow Cooker french Onion Soup

You're going to love the taste of this Slow Cooker french Onion Soup. Loaded with caramelized onions and Gruyere cheese. One bowl just isn't going to be enough!

5 from 1 vote

Print Pin Rate

Course: Soups

Cuisine: American

Servings: Servings

Author: Rob

Ingredients

3 lbs. yellow onions, peeled and sliced
2 tbsp. melted butter
2 tbsp. olive oil
2 tsp. kosher salt
Freshly ground black pepper
10 cups beef broth
2 tbsp. balsamic vinegar

To Serve

4-6 toasted french bread slices
1 ½ -2 cups shredded Gruyere, mozzarella or Asiago cheese or a mix of all

Instructions

Place the sliced onions in a 5 qt. or larger slow cooker.
Drizzle over the butter and olive oil.
Sprinkle the salt and pepper over the top and cook on LOW for 12 hours.
Add in the broth and balsamic vinegar.
Stir and cook on LOW for an additional 8 hours.
Preheat oven to 350F.
Arrange 4-6 oven safe bowls on a sturdy baking sheet.
Ladle the soup into the bowls.
Top with a slice of toasted french bread and 1/3 cup of cheese each. Add more cheese if you like.
Bake 20-25 minutes or until the cheese is browned to your liking.
Cool 2-3 minutes before serving.

Slow Cooker French Onion Soup