Slow Cooker French Onion Soup

We finally (!!!) just had our first semi-chilly day in Tulsa, and you should have seen me… totally pulled out the boots and turtleneck! You would have thought we were experiencing an arctic blast, when it was actually just under 60 degrees. It’s amazing how the changing temps cause such a shift in what I’m craving for dinner, and the most visible evidence is the return of my slow-cooker to the countertop. There’s something so comforting about putting all the ingredients in the cooker in the morning, turning it on low heat, and then coming home to the most amazing smells before you even open the front door.

For me, the best slow-cooker recipes are those where you can toss all the ingredients into the cooker at once, turn it on, then let it do its thing. After all, isn’t one of the main benefits of this type of cooking that it’s no-fuss and results in fewer dishes to clean at the end of the day? This French Onion Soup is one of those; the only prep that it requires is chopping up an onion and opening a few boxes of broth! It really is that easy, and after hanging out in the slow-cooker for 9 hours, it tastes like you’ve been slaving over the stove all day.

When I discovered that you can make caramelized onions in the slow cooker with no stirring and virtually no work, well, I was sold!

It was a huge hit!!! And I cannot wait to make this again!!

How To Make French Onion Soup in the Slow Cooker

Serves 6 to 8

What You Need


  • 3 pounds 

    yellow onions, peeled, sliced, and cut into quarter-moons

  • 2 tablespoons 

    unsalted butter, melted

  • 2 tablespoons 

    olive oil

  • 2 teaspoons 

    kosher salt, plus more as needed

  • Freshly ground black pepper

  • 10 cups 

    reduced-sodium beef broth

  • 2 tablespoons 

    balsamic vinegar

  • 3 tablespoons 

    brandy (optional)

    To Serve

  • 4 to 6 

    toasted baguette slices per bowl

  • 1/3 cup 

    grated Gruyère cheese per bowl (1 1/3 to 2 cups total)


  • Cutting board and chef's knife

  • 5-quart or larger slow cooker

  • Wooden spoon

  • Oven-safe soup bowls

  • Rimmed baking sheet


  1. Season the onions. Place the onions in a 5-quart or larger slow cooker. Stir in the butter, oil, salt, and a generous amount of pepper.

  2. Add the broth and the vinegar. Stir in the broth and vinegar.

  3. Cook on high for 9 hours or more. Longer cooking will only intensify the flavors. Taste and season with more salt and pepper if needed, and stir in the brandy if using.

  4. Portion the soup into oven-safe bowls. Arrange a rack in the upper third of the oven and heat to 350°F. Ladle the soup and onions into oven-safe soup bowls and place the bowls on a rimmed baking sheet.

  5. Top with toast and shredded cheese. Top each bowl with a slice of toast and a generous quantity of shredded Gruyère cheese, about 1/3 cup per bowl.

  6. Bake for 20 to 30 minutes. Bake until the cheese is completely melted, 20 to 30 minutes.

  7. Broil for 2 to 3 minutes. Turn the oven to broil. Broil until the cheese is bubbling and browned, 2 to 3 minutes. Remove from the oven and let cool for a few minutes. Serve with chopped fresh shallot or onion if desired.

Adjusting Consistency & Thickness: When I have made this, the soup has always been just the right consistency. But if yours seems a little thin or watery, you can quickly finish it off on the stovetop by simmering gently in a saucepan for 15 minutes or until the broth has reduced a little.

So so amazingly delicious!!!!! I cannot wait to see what you think!

And I’d love to hear in the comments — what’s your favorite slow-cooker recipe this fall?


For more of my slow cooker recipes click here.

Sam’s Soup Favorites: