Slow Cooker French Onion Soup

This Slow Cooker French Onion Soup is a cozy, comforting bowl of caramelized onions, rich vegetable broth, and gooey melted Gruyère cheese. Made entirely in the slow cooker, it’s a hands-off recipe that fills your kitchen with irresistible aromas and delivers deep, savory flavors with minimal effort.

Why You’ll Love This Recipe

• Effortless Comfort Food: Let your slow cooker do all the work while you relax.

• Deep, Rich Flavor: Slow-cooked onions caramelize naturally, giving the soup a sweet and savory depth.

• Perfect for Any Occasion: Elegant enough for a dinner party, yet simple enough for a weeknight treat.

• Customizable: Easy to adapt with vegan cheese or gluten-free bread options.

• Crowd-Pleaser: Gooey cheese and crispy toasted baguette slices make everyone happy.

Ingredients

(Tip: You’ll find the full list of ingredients and measurements in the recipe card below.)

• 4 yellow onions, thinly sliced

• 2 tbsp butter, or olive oil for a 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, substitute with 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

Directions

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

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

3. Deglaze with balsamic vinegar and sherry, scraping up any 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 the oven to 400°F (200°C). Slice and toast the baguette until golden and crispy.

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

7. Place bowls under the broiler for a few minutes until the cheese melts and bubbles. Serve with extra thyme or a drizzle of balsamic reduction if desired.

Servings and Timing

• Servings: 6

• Prep Time: 15 minutes

• Cook Time: 10 minutes

• Slow Cooker Time: 5 hours

• Total Time: 5 hours 25 minutes

Variations

• Vegan: Use olive oil instead of butter and a plant-based cheese.

• Gluten-Free: Serve with gluten-free bread or croutons.

• Add Wine: Replace sherry with white wine for a different depth of flavor.

• Herb Twist: Add rosemary or tarragon for a unique aroma.

• Cheese Swap: Try Fontina or Emmental instead of Gruyère.

Storage/Reheating

• Fridge: Store in an airtight container for up to 3 days.

• Freezer: Can be frozen for up to 2 months (omit baguette; add fresh when serving).

• Reheating: Heat on the stove over medium-low until warmed through. Top with freshly toasted bread and cheese when ready to serve.

FAQs

1. Can I make this soup without a slow cooker?

Yes! You can caramelize onions on the stovetop over low heat for 45–60 minutes, then add the remaining ingredients and simmer for 30–40 minutes.

2. Can I use yellow onions only, or mix with other types?

Yellow onions are ideal for caramelization, but mixing with sweet onions or red onions can add a unique flavor.

3. Do I have to use sherry?

Sherry is optional but adds depth. You can substitute with white wine or skip it entirely.

4. Can I prepare this soup ahead of time?

Absolutely. Make the soup a day in advance and refrigerate. Reheat gently on the stove before serving.

5. How do I prevent the cheese from burning under the broiler?

Place the oven rack a few inches below the broiler and watch closely. Broil just until the cheese melts and bubbles.

6. Can I use pre-shredded cheese?

Yes, but freshly shredded cheese melts better and creates a creamier texture.

7. How do I make this soup vegan?

Use olive oil instead of butter and vegan cheese or nutritional yeast for the topping.

8. Can I add meat like beef or chicken?

Traditionally French onion soup is vegetarian, but adding shredded rotisserie chicken or bacon can give extra protein and flavor.

9. Can I freeze the soup with the bread and cheese?

It’s best to freeze the soup without bread and cheese. Add fresh bread and cheese when reheating.

10. How can I make the soup sweeter or richer?

Use a pinch more sugar while caramelizing onions or add a splash of balsamic reduction at the end.

Conclusion

This Slow Cooker French Onion Soup is the ultimate comfort dish—rich, flavorful, and effortless. Perfect for a chilly evening, a dinner party, or meal prepping for the week, it delivers warm, cheesy satisfaction in every bite. Whether you stick to the classic recipe or try one of the variations, this soup will quickly become a family favorite.

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