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. A few weeks ago we walked through the classic, Julia-informed way to make this bistro favorite. But you know what? Now that I know how to make it in the slow cooker, I'm probably never going back.
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?
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 dinner time, ladle out soup, and broil with cheese and toast.
Perfect French onion soup, absolutely hands-off. This is why slow cookers exist, you guys.
More on French Onion Soup
This is a pretty quick and basic guide to making French onion soup. If you want a little more detail, like some of my favorite flavoring add-ins (star anise, cinnamon, rosemary), my opinions on the right ratio of cheese to soup, and other notes on the classic preparation, visit our main French onion soup tutorial.
How To Make French Onion Soup in the Slow Cooker
What You Need
3 pounds yellow onions, peeled, sliced, and cut into quarter-moons
2 tablespoons unsalted butter, melted
2 tablespoons olive oil
1 teaspoon salt, plus more to taste
Freshly ground black pepper
2 tablespoons balsamic vinegar
3 tablespoons brandy, optional
Cutting board and chef's knife
Oven-safe soup bowls
- Season the onions: Place the onion slices in a 5-quart (or larger) slow cooker. Stir in the butter and olive oil, salt, and a generous quantity of black pepper.
- Cook on LOW for 12 hours: Cover and cook on LOW overnight or for 12 hours. The onions should be dark golden brown and soft.
- Add broth: Stir in the balsamic vinegar and the broth.
- Cook for 6 to 8 hours on LOW: Cover and continue cooking on LOW 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 desired, and stir in the brandy if using.
- Portion the soup into oven-safe bowls: Heat the oven to 350°F. Ladle the soup and onions into oven-safe bowls and place the bowls in a baking pan.
- Top with toast and shredded cheese: Top each bowl with a slice of toast and a generous quantity of shredded Gruyere cheese.
- Bake for 20 to 30 minutes: Bake on a rack in the upper third of the oven until the cheese is completely melted.
- Broil for 2 to 3 minutes: Turn the oven to broil and broil the soup for 2 to 3 minutes or until the cheese is bubbling and browned. Remove from the oven and let cool for a few minutes, then serve with chopped fresh onion on the side.
- 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.
- Nutrition Note: The nutrition info below does not include the bread and Gruyere for topping the soup.
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