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French Onion Soup topped with melted Gruyere cheese and fresh thyme in a cast iron pot

French Onion Soup (Stovetop & Slow Cooker)

Emily Wilson
This classic French onion soup features deeply caramelized onions, rich beef broth, toasted baguette, and golden melted Gruyere cheese. Includes both stovetop and slow cooker methods, plus lighter swaps for a healthier version.
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Prep Time 15 minutes
Cook Time 1 hour 30 minutes
Total Time 1 hour 45 minutes
Course Main Course
Cuisine French
Servings 4 bowls
Calories 520 kcal

Equipment

  • Large heavy bottom pot or Dutch oven
  • Wooden Spoon
  • Sharp knife
  • Slow cooker or crockpot
  • Oven safe soup bowls
  • Baking Sheet

Ingredients
  

Soup Base

  • 6 cups Yellow onions, thinly sliced About 5 to 6 large onions
  • 2 tablespoons Unsalted butter
  • 1 tablespoon Olive oil
  • 1 teaspoon Salt Plus more to taste
  • 2 cloves Garlic, minced
  • 4 cups Beef broth High quality recommended
  • 1/2 cup Additional beef broth For deglazing
  • 1 teaspoon Apple cider vinegar
  • 1 Bay leaf
  • 2 sprigs Fresh thyme Or 1/2 teaspoon dried thyme

Topping

  • 4 slices Baguette About 1/2 inch thick
  • 1 1/2 cups Gruyere cheese, grated Swiss can be substituted

Instructions
 

  • Stovetop Method: Heat butter and olive oil in a large pot over medium heat. Add sliced onions and salt. Reduce heat to medium low and cook for 45 to 60 minutes, stirring every 5 to 10 minutes, until deeply golden and soft.
    Add garlic and cook for 30 seconds. Pour in 1/2 cup beef broth and apple cider vinegar to deglaze, scraping the bottom of the pot. Add remaining broth, bay leaf, and thyme. Bring to a gentle boil, then simmer for 20 to 25 minutes. Season to taste.
    Toast baguette slices at 375°F for about 8 minutes. Ladle soup into oven safe bowls, top with bread and grated cheese, and broil for 3 to 5 minutes until melted and golden.
    Slow Cooker Method: Lightly sauté onions in butter and oil for 15 to 20 minutes. Transfer to slow cooker. Add broth, garlic, bay leaf, thyme, and vinegar. Cook on low for 6 to 8 hours or high for 3 to 4 hours. Finish with toasted bread and cheese under the broiler before serving.

Notes

For a healthier French onion soup, reduce the cheese slightly and use low sodium broth. Freeze the soup base without bread and cheese for up to 3 months. Always broil the cheese topping just before serving for best texture.
Nutrition Facts
•Calories: 520 kcal 
•Carbohydrates: 38g 
•Protein: 22g 
•Fat: 28g 
•Saturated Fat: 14g 
•Cholesterol: 65mg 
•Sodium: 820mg 
•Potassium: 900mg 
•Fiber: 5g 
•Sugar: 9g 
•Vitamin A: 700 IU 
•Vitamin C: 18mg 
•Calcium: 550mg 
•Iron: 2mg