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Slow Cooker French Onion Soup

A heartwarming soup filled with sweet caramelized onions, aromatic herbs, and gooey melted cheese atop crusty bread.
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Prep Time 20 minutes
Cook Time 6 hours
Total Time 6 hours 20 minutes
Servings: 4 servings
Course: Appetizer, Soup
Cuisine: Comfort Food, French
Calories: 350
Ingredients Method Notes

Ingredients
  

Main Ingredients
  • 4 large onions, thinly sliced Use yellow onions for sweetness
  • 4 cups beef broth (or vegetable broth for a vegetarian version) Ensure broth is flavorful
  • 2 tablespoons olive oil For sautéing
  • 2 teaspoons sugar To help caramelize the onions
  • 1 teaspoon salt
  • 1 teaspoon dried thyme
  • 1 bay leaf
  • 1 tablespoon balsamic vinegar (optional) For depth of flavor
  • 4 slices French baguette For serving
  • 1 cup shredded Gruyère cheese (or mozzarella for a milder flavor)

Method
 

Preparation
  1. In a large skillet over medium heat, add olive oil. Toss in the sliced onions, sugar, and salt. Sauté until the onions soften and turn golden brown, about 20 minutes.
  2. Transfer the caramelized onions to the slow cooker. Add in the beef (or vegetable) broth, thyme, bay leaf, and balsamic vinegar if using. Stir well to combine.
  3. Cover and cook on low for 5-6 hours or on high for 3-4 hours. The longer it simmers, the better the flavors meld together.
  4. About 30 minutes before serving, toast the slices of French baguette until golden and crispy.
  5. When ready, carefully remove the bay leaf from the soup. Ladle the soup into bowls and top each with a slice of toasted baguette. Sprinkle generously with shredded Gruyère cheese. For an extra special presentation, you can broil them for a minute to melt the cheese.

Notes

Storage Tip: Leftovers can be stored in an airtight container in the refrigerator for up to 3 days. For freezing, keep in a freezer-safe container for up to 3 months. Reheat gently on the stove or microwave.