Slow Cooker French Onion Soup

4 servings
12 hr
A bowl of crock pot French onion soup.

Easy Slow Cooker French Onion Soup

Traditionally, French onion soup is made by cooking onions for a long time on the stovetop over low heat until they are rich golden brown. This makes a delicious, flavorful broth, but it's also time-consuming and requires you to be home for the several hours that the onions are cooking.

Cooking the onions all day in a slow cooker is SO much easier and still produces a delicious, flavorful French onion soup.

It's important to get your onions in the slow cooker early in the day. Getting that lovely golden color and rich flavor requires the onions to cook for about 10 hours in your slow cooker on high heat. You can also cook the onions up to 3 days in advance if you like. So, if you're the kind of person that likes to do some meal prep on the weekends, cooking onions all day on a Saturday or Sunday will make weeknight French onion soup a snap.

French onion soup is a baked soup topped with cheese and croutons. It works best to bake the soup in individual bowls or pots. You can use ramekins, oven-proof soup bowls, or get all fancy and traditional with these adorable lion's head soup bowls.

lions head soup bowls

Making French onion soup requires a LOT of onions. This recipe uses 8 pounds, which is actually more than you need if you're only making French onion soup.

Also, I like a lot of onions in my French onion soup. But, please feel free to use fewer onions if you prefer your soup to have a higher proportion of broth to onions.

Regardless of how many onions you're using, it's a lot of chopping. I find using a food processor to slice the onions invaluable. If that sounds good to you, peel and cut the onions into quarters and then slice them using the 4MM slicing blade of your food processor.

A bowl of crock pot French onion soup.
A spoonful of crock pot French onion soup.
Slow Cooker French Onion Soup
Recipe details
  • 4  servings
  • Prep time: 60 Minutes Cook time: 11 Hours Total time: 12 hr
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  • 6 lbs yellow onions
  • 5 tablespoon butter, cut into 5 pieces
  • 1 ½ teaspoon all-purpose flour
  • 4 cups chicken broth
  • 4 cups beef broth
  • ½ cup dry white wine
  • 2 teaspoons dried thyme
  • 1 bay leaf
  • Salt and pepper, or to taste
  • 8 oz grated gruyere cheese
  • About 1 cup of Croutons

Peel the onions and cut them into quarters. Using a sharp knife, cut each quarter into slices, approximately ¼ inch wide. Alternatively, use the 4 MM slicing blade of your food processor to cut the onion quarters into slices.
Pile the sliced onions into a slow cooker.  The pot will be quite full of onions. Use your hands to press them down if the pot is over flowing. Scatter the pieces of butter over the top of the onions and sprinkle with about 1 teaspoon salt. Cover, and cook on high for 10 hours, at which point the onions should be a rich golden color.
Dump the onions into a large heavy bottom sauce pan or dutch oven. (If you are planning to use some of the onions later in the week for Pot Roast Sandwiches and Creamy Chicken and Rice, remove 1 ½ cups of the onions and store in an airtight container in the refrigerator.)
Sprinkle the flour over the top of the onions and cook over medium-high heat for 2-3 minutes, stirring constantly. Stir in the chicken and beef broth, wine, thyme, bay leaf, and about 1 teaspoon each salt and pepper. Bring to a boil and allow to simmer uncovered, stirring occasionally, for 30-45 minutes, until the liquid has reduced by about a third and the broth has thickened slightly. Taste, and add more salt and pepper if desired.
Preheat the broiler.
Remove the pan from the heat and ladle the hot soup into 4 soup bowls, filling each to within about 1-inch of the top. Place the soup bowls on a baking sheet. Top each with several croutons - enough to cover the surface of the soup. Distribute the grated cheese amongst the 4 bowls, covering the croutons.
Slide the baking sheet with the soup bowls into the oven under the broiler and cook for a couple of minutes, until the cheese is melted, bubbling, and just beginning to brown. *Watch carefully. The cheese will go from brown to burnt in an instant.
Carefully remove from the oven. Use oven mitts to place each soup bowl on a plate and serve
  • Gruyere cheese is incredibly delicious melted over French onion soup. It's also quite expensive. If you'd rather use a different cheese, Swiss, Asiago, Mozzarella, or Pecorino Romano also work well. Or any combination of the above.
Rebecca Blackwell | A Little and A Lot
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