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4.50 from 6 votes

Slow Cooker French Onion Soup

Let your appliance do all the hard work to make this spectacular slow cooker French onion soup! It's rich and flavourful, and topped with a giant cheesy crouton.
Prep Time15 minutes
Cook Time9 hours
Total Time9 hours 15 minutes
Course: Main meals
Cuisine: French
Diet: Vegetarian
Servings: 2 people
Calories: 488kcal
Author: Becca Heyes


For the slow cooker French onion soup:

  • 4 large onions sliced
  • 30 g (~ 2 tbsp) butter, roughly chopped
  • 1 tablespoon caster sugar (optional)
  • 1 tablespoon balsamic vinegar
  • 2 teaspoon minced garlic or garlic puree
  • 1 teaspoon dried thyme
  • 1 teaspoon black pepper
  • 750 ml (~ 3 cups) vegetable stock

For the cheesy crouton:

  • 2-4 thick slices French baguette
  • 2-4 tablespoon grated cheese (I used cheddar)


  • Add all of the soup ingredients to a slow cooker, and mix well to break up the onions. Cook on high for approximately 9 hours, or until the onions are a deep, rich brown colour, and very soft.
  • Serve on its own, or with a cheesy crouton. To make the cheesy crouton, dish up a bowlful of soup into a heat-safe bowl, and top with 1 or 2 thick slices of French baguette. Sprinkle over plenty of grated cheese, then place under a grill (broiler) for a few minutes, until the cheese is melted and slightly crispy. Serve immediately.


Serving: 1bowl | Calories: 488kcal | Carbohydrates: 65.1g | Protein: 14.8g | Fat: 20.1g | Saturated Fat: 12.2g | Cholesterol: 53mg | Sodium: 536mg | Potassium: 557mg | Fiber: 8.1g | Sugar: 20.1g | Calcium: 258mg | Iron: 4mg