How To Make French Onion Soup
When I discovered that you can make caramelized onions in the slow cooker with no stirring and virtually no work, it was only a small step from there to French onion soup. Although I’ve made this bistro favorite the classic, Julia-inspired way, now that I know how to make it in the slow cooker, I’m probably never going back to stovetop!
Here’s a step-by-step recipe for blissfully delicious French onion soup made from start to finish in the slow cooker. Well, right up until the cheesy toast. You still need the oven for that, but with soup this easy, what’s a little broiling at the end?
Why the Slow Cooker Makes the Best French Onion Soup
This is one of those magical recipes that makes you say Oh, can it be so easy? And the answer to that, for once, is yes. Yes it can.
Here’s how it goes: Throw a few pounds of sliced onions in the slow cooker overnight, or for 12 hours (you can slice them in your food processor if you really want to hurry this along). Cook until dark and jammy; you don’t even need to stir. Pour in some broth and walk away again. Come back at dinnertime, ladle out soup, and broil with cheese and toast.
Perfect French onion soup, absolutely hands-off. This is why slow cookers exist, you guys.
For Your Information
This recipe calls for three pounds of yellow onions and 10 cups of beef broth. Sweet onions are marvelous here if you can get them. Feel free to use a combination of yellow and red onions, if needed.
The onions cook alone for 12 hours. Opt for cooking overnight if you plan to serve the soup for dinner the next day. After adding the broth and seasoning to the soup, cook agin for another six to eight hours. The total cook time for this recipe is about 20 hours in the slow cooker.
You will smell this soup cooking. But it smells delicious, so it’s OK!
- 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)
- Chopped shallot or fresh onion (optional)
- Cutting board and chef's knife
- 5-quart or larger slow cooker
- Wooden spoon
- Oven-safe soup bowls
- Rimmed baking sheet
- 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.
- Cook on LOW for 12 hours. Cover and cook on the LOW setting overnight until the onions should be dark golden-brown and soft, 12 hours or overnight.
- Add the broth and vinegar. Stir in the broth and vinegar.
- Cook for LOW 6 to 8 hours. Cover and continue cooking on the LOW setting for 6 to 8 hours. This is flexible; as long as your slow cooker holds moisture well (wrap a towel over the lid if quite a lot of steam escapes), you can cook the soup for hours. Longer cooking will only intensify the flavors. Taste and season with more salt and pepper if needed, and stir in the brandy if using.
- 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.
- 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.
- Bake for 20 to 30 minutes. Bake until the cheese is completely melted, 20 to 30 minutes.
- 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.