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Slow Cooker French Onion Soup

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This Slow Cooker French Onion Soup is a rich, comforting blend of caramelized onions, savory vegetable broth, and melted Gruyère cheese. Made entirely in the slow cooker, it’s a hands-off recipe that fills your kitchen with irresistible aromas. Perfect for weeknight dinners, cozy evenings, or elegant gatherings, this soup delivers deep, savory flavor with minimal effort.

  • Author: Chef Sarah
  • Prep Time: 15 minutes
  • Cook Time: 10 minutes
  • Total Time: 5 hours 25 minutes
  • Yield: 6 servings
  • Category: Soup
  • Cuisine: French, American

Ingredients

4 yellow onions, thinly sliced

2 tbsp butter (or olive oil for vegan option)

4 cloves garlic, minced

1 tbsp sugar

1 tbsp balsamic vinegar

2 tbsp dry sherry (optional)

8 cups vegetable broth, low-sodium

2 sprigs fresh thyme (or 1 tsp dried thyme)

2 bay leaves

½ teaspoon salt

¼ teaspoon black pepper, adjust to taste

1 tbsp soy sauce (or tamari for gluten-free)

1 baguette, sliced

2 cups Gruyère cheese, freshly shredded

Instructions

  1. Set slow cooker to high. Add butter (or olive oil), sliced onions, and sugar. Stir to coat. Prop lid slightly open and cook on low for 6–8 hours, stirring occasionally, until onions are golden and soft.

  2. Add minced garlic and cook 2–3 minutes on low.

  3. Deglaze with balsamic vinegar and sherry, scraping up browned bits.

  4. Add vegetable broth, thyme, bay leaves, soy sauce, salt, and pepper. Cover and cook on low for another 4–6 hours.

  5. Preheat oven to 400°F (200°C). Slice and toast baguette until golden.

  6. Remove thyme sprigs and bay leaves. Ladle soup into oven-safe bowls, top with toasted baguette slices, and sprinkle with Gruyère.

  7. Broil for a few minutes until cheese melts and bubbles. Serve immediately, optionally garnished with extra thyme or balsamic drizzle.

Notes

  • Vegan: Use olive oil instead of butter and plant-based cheese.
  • Gluten-Free: Serve with gluten-free bread or croutons.
  • Herb Twist: Try rosemary or tarragon for unique flavor.
  • Cheese Swap: Fontina or Emmental can replace Gruyère.

Find it online: https://cookingwithsarah.com/slow-cooker-french-onion-soup/