Weeknight French Onion Soup

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5 from 1 reviews

Classic French onion soup made easy thanks to the slow cooker. You can caramelize the onions ahead of time in the slow cooker so all you need is 30 minutes the next day to add the finishing touches. Perfect for a weeknight supper!



For the Caramelized Onions

  • 2 pounds white onions, thinly sliced
  • 1/4 cup unsalted butter, cut into chunks
  • 4 sprigs fresh thyme
  • 1 teaspoon salt

For the Soup

  • 1/2 cup dry white wine
  • 1 tablespoon flour
  • 1 (32-oz) box of beef broth (see note)
  • 1 bay leaf
  • 1 tablespoon Worcestershire sauce
  • 8 slices French bread (see note), toasted
  • 8 ounces Gruyere cheese, grated


  • Place the sliced onions, butter, thyme, and salt into the slow cooker. Toss it all together and then cover and cook on low for 10-12 hours. I stir them a couple of times as they are cooking. Once the onions have cooked discard the thyme sprigs and transfer the onions (and all of the liquid) to a bowl. Cover and refrigerate until you’re ready to make the soup.
  • To make the soup. First, heat the onions and all of their liquid over medium heat in a 5-quart pot. Add the wine and simmer it for a few minutes with the onions. Sprinkle one tablespoon of flour over the top and give it all a stir. Add the beef stock, bay leaf, and Worcestershire sauce to the pot. Raise the heat until the soup is at a strong simmer and then lower the heat to maintain a gentle simmer.
  • Once the soup has simmered for 20 to 30 minutes, check the seasoning and add additional salt, if needed. Ladle the soup into oven-safe bowls.
  • Place bread slices on top of each soup and top each with the grated cheese. Place the bowls on a baking sheet lined with tin foil. Place the bowls under the broiler for a few minutes (keep a close eye on them) until the cheese is melted and bubbly. Remove and serve immediately.


  • I used regular beef broth for this recipe, so if you use low-sodium beef broth you made need to adjust the salt level of your soup so be sure to taste it while it’s simmering to make any adjustments.
  • I used eight slices of bread from a thin baguette which was approximately 16 ounces of bread. Depending on the type of bread you use the nutrition estimate may vary.


Keywords: easy french onion soup, slow cooker french onion soup