How To Make French Onion Soup in the Slow Cooker

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?

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.

• 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!

• Slice the onions into quarter-moons. You can use your mandoline, a food processor, or a chef’s knife to make quick work of this.
• Cook the onions with butter and salt on low for 12 hours: This step is going to perfume the whole house. A reader suggested doing this step on a screened-in porch or in your garage if you need to avoid your home smelling like cooking onions for a whole day.
• Add the broth and vinegar and cook for six to eight more hours on low: Again this can be done without supervision; there’s no stirring or checking.
• Top with toasted bread and Gruyère and bake before serving: This final step really helps to thicken the soup. The baking allows for more evaporation and some of the starch from the bread softens and thickens the soup as well.

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.

Get the recipe: How To Make French Onion Soup