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slow cooker french onion soup

This slow cooker French onion soup is comforting and full of flavor, featuring caramelized onions, rich broth, and cheesy toasts. Perfect for chilly evenings, this hands-off recipe allows you to enjoy the warm, savory dish without spending hours in the kitchen.
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Prep Time 15 minutes
Cook Time 4 hours
Total Time 8 hours 15 minutes
Course Soup
Cuisine French
Servings 4 People
Calories 250 kcal

Equipment

  • 1 slow cooker
  • 1 large skillet
  • 1 wooden spoon
  • 1 cutting board
  • 1 ladle
  • 1 oven-safe bowls

Ingredients
  

  • 5 large onions, thinly sliced
  • 4 tablespoons unsalted butter
  • 1 tablespoon olive oil
  • 2 teaspoons salt
  • 1 teaspoon sugar
  • 4 cloves garlic, minced
  • 8 cups beef broth
  • 1 cup dry white wine optional
  • 2 teaspoons fresh thyme leaves or 1 teaspoon dried thyme
  • 1 teaspoon black pepper
  • 12 slices French baguette
  • 2 cups shredded Gruyère cheese or a mix of Gruyère and Swiss

Instructions
 

  • In a large skillet, melt the butter and olive oil over medium heat. Add the sliced onions and salt. Stir to coat the onions with the butter and oil.
  • Cook the onions for about 15-20 minutes, stirring frequently, until they start to caramelize. Add the sugar and minced garlic, cooking for another 3-4 minutes until the onions are golden brown.
  • Transfer the caramelized onions to the slow cooker. Add the beef broth, white wine (if using), thyme, and black pepper. Stir to combine.
  • Cover the slow cooker and cook on low for 8 hours or on high for 4 hours, until the flavors meld together and the onions are very soft.
  • When ready to serve, preheat the oven broiler. Arrange the baguette slices on a baking sheet and toast them under the broiler until they are golden brown on both sides.
  • Ladle the soup into oven-safe bowls, top each with 2-3 slices of toasted baguette, and sprinkle generously with shredded Gruyère cheese.
  • Place the bowls under the broiler for a few minutes, until the cheese is melted and bubbly. Be careful not to burn the cheese.
  • Remove from the oven and let cool slightly before serving.

Notes

You can omit the wine if you prefer a non-alcoholic version.
For extra depth of flavor, consider adding a splash of balsamic vinegar before serving.
This soup can be made ahead and stored in the refrigerator for up to 3 days or frozen for up to a month. Reheat on the stove or in the microwave before serving.