Name: Slow Cooker French Onion Soup
Prep time: 25 min
Cook time: PT-487092H6M13S
Total time: PT-487092H6M13S
Cuisine: French
Ingredients: 4 large sweet onions (Vidalia or yellow), thinly sliced; 4 tablespoons unsalted butter; 1 tablespoon olive oil; 1 teaspoon sugar; 4 cloves garlic, minced; 8 cups beef or vegetable broth; 1 cup dry white wine (or extra broth); 2 teaspoons fresh thyme leaves; Salt and pepper, to taste; 1 baguette, sliced; 2 cups shredded Gruyère cheese

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This Slow Cooker French Onion Soup brings deep, sweet caramelized onions together with savory broth, a crusty baguette, and melty Gruyère cheese. It’s a classic comfort dish—made easy with hands-off slow cooker magic!

Why You’ll Love This Recipe

Hands-Off Comfort: Caramelize onions, then let the slow cooker do all the work.
Classic French Flavors: Sweet onions, thyme, and rich broth finished with broiled cheese.
Restaurant-Quality At Home: Impressive, cozy, and deliciously cheesy.
Perfect For Make-Ahead: Soup can be made ahead and topped/broiled just before serving.

Ingredients

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

4 large sweet onions (Vidalia or yellow), thinly sliced
4 tablespoons unsalted butter
1 tablespoon olive oil
1 teaspoon sugar
4 cloves garlic, minced
8 cups beef or vegetable broth
1 cup dry white wine (or more broth)
2 teaspoons fresh thyme leaves
Salt and pepper, to taste
1 baguette, sliced
2 cups shredded Gruyère cheese

Directions

Caramelize Onions:
Melt butter with olive oil in a large skillet over medium heat. Add sliced onions and sugar. Cook, stirring, for 15–20 minutes until golden and soft.
Add Garlic:
Stir in minced garlic and cook for 1–2 minutes until fragrant.
Transfer To Slow Cooker:
Pour caramelized onions and garlic into the slow cooker. Add broth, wine, thyme, salt, and pepper. Stir to combine.
Slow Cook:
Cover and cook on low for 6–8 hours or high for 3–4 hours.
Toast Baguette:
About 30 minutes before serving, preheat oven to 400°F (200°C). Slice the baguette and toast for 5–7 minutes until golden.
Assemble Bowls:
Ladle soup into oven-safe bowls. Top with toasted baguette slices and shredded Gruyère.
Broil:
Place bowls under broiler for 2–3 minutes, or until cheese is bubbly and golden.
Serve:
Carefully remove from oven and serve hot, garnished with extra thyme if desired.

Servings And Timing

Servings: 6
Prep Time: 25 minutes
Cook Time: 6–8 hours (low) or 3–4 hours (high)
Total Time: 6½–8½ hours (mostly hands-off)

Variations

Vegetarian: Use high-quality vegetable broth instead of beef broth.
Cheese Swap: Try Swiss or mozzarella if Gruyère isn’t available.
No Wine: Replace wine with extra broth and a splash of lemon juice or white wine vinegar for acidity.
Herb Boost: Add a bay leaf or sprinkle with fresh parsley before serving.

Storage/Reheating

Refrigeration: Store soup (without bread/cheese) in an airtight container for up to 4 days.
Freezing: Soup base freezes well (up to 2 months). Add fresh bread and cheese before broiling.
Reheating: Warm soup gently on the stove or in the microwave. Top with fresh toasted bread and cheese, then broil to serve.

FAQs

1. Can I Skip Caramelizing The Onions?

Caramelizing creates deep flavor and is worth the extra step—but you can start them in the slow cooker if short on time (they will be softer and less browned).

2. Is This Recipe Gluten-Free?

Use gluten-free baguette slices for a GF version.

3. Can I Make This Without Oven-Safe Bowls?

Top soup with toast and cheese on a baking sheet, broil, then transfer to bowls.

4. What’s The Best Onion To Use?

Vidalia or yellow onions are ideal for sweet, balanced flavor.

5. How Can I Make It Extra Rich?

Add a splash of Worcestershire sauce or a few dashes of balsamic vinegar to the broth.

6. Can I Use Another Cheese?

Swiss, provolone, or even sharp cheddar will work in a pinch.

7. How Do I Keep Bread From Sinking?

Use sturdy bread and broil it on top of the soup right before serving.

8. Can I Double The Recipe?

Yes, use a large slow cooker and adjust seasoning to taste.

9. Can I Prep Ahead?

Soup base can be made 2–3 days in advance; toast and broil with cheese just before serving.

10. What Sides Go Well?

Serve with a simple green salad or roasted veggies for a complete meal.

Conclusion

Slow Cooker French Onion Soup is the ultimate cozy classic, made easy for any night of the week. With deep, caramelized flavor and gooey cheese, it’s a show-stopper for family, guests, or just yourself. Enjoy the slow-cooked comfort and classic French flair in every bite!

Maggie