This is my all-time favorite soup, straight from the Bored of Lunch cookbook: this Slow Cooker French Onion Soup is made with onions, butter, Italian seasoning, garlic, brown sugar, and white wine.

To make this savory French Onion Soup in your slow cooker or crockpot, simply combine the ingredients and cook on high for 10 hours. Then, add stock and Worcestershire sauce, and broil with bread and cheese for 8-10 minutes.

I fell in love with this recipe the first time I tried it. The aroma of caramelized onions and the cheesy topping adds a perfect finishing touch, making it a comforting meal for any occasion.

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How can I prevent the onions from burning during slow cooking?

To prevent burning, make sure to stir the onions occasionally during the cooking process. Additionally, consider using a slow cooker with a timer function to avoid overcooking. Keeping the heat on low and adding a bit of water can also help maintain moisture.

Can I use a different type of cheese for the topping?

Yes, you can customize the cheese topping to your preference. While gruyère cheese is traditional, you can use alternatives like Swiss cheese or even cheddar for a unique flavor. Experiment with different cheeses to find your favorite combination.

Slow Cooker French Onion Soup Ingredients

• 10 onions, thinly sliced
• 100g of low-fat butter
• 1 tbsp of Italian herb seasoning
• 2 cloves of garlic, crushed
• 1 bay leaf
• 2 tbsp of brown sugar
• 200ml of white wine
• 900ml of vegetable or beef stock
• 1 tsp of Worcestershire sauce
• Salt and pepper, to taste
• Slices of baguette
• 120g of gruyère cheese, grated

How To Make Slow Cooker French Onion Soup

1. Prep the base: In your slow cooker, combine the sliced onions, butter, Italian herb seasoning, crushed garlic, bay leaf, and brown sugar. Pour in the white wine, and give everything a good stir. Season with salt and pepper to taste.
2. Cook it slow: Set your slow cooker to high and let the onion mixture cook for 10 hours. The long cooking time helps the onions caramelize beautifully, drawing out their natural sweetness and enhancing the soup’s flavor.
3. Enrich the soup: After 10 hours, pour in the vegetable or beef stock along with the Worcestershire sauce. Stir well to mix all the ingredients thoroughly.
4. Prep for crunch and cheese: If your slow cooker is ovenproof, skip to the next step. If not, carefully transfer the hot soup into an ovenproof dish.
5. Cheese the bread: Lay the baguette slices on top of the soup. Evenly sprinkle the grated gruyère cheese over the bread.
6. Golden topping: Place the slow cooker insert or ovenproof dish under a preheated grill. Cook for 8-10 minutes or until the cheese is melted and golden brown, watching carefully to prevent burning.

Recipe Tips

• Enhance flavors: Consider caramelizing the onions on the stove before adding them to the slow cooker for a deeper, richer flavor.
• Avoid burning: Keep the grill watchful eye during the final browning step; this prevents the cheese from burning and turning bitter.
• Cheese choices: If gruyère cheese is too strong for your taste, try mozzarella for a milder, gooey topping.
• Bread alternatives: Replace the traditional baguette with a thicker slice of sourdough bread for a heartier texture and tangy twist.
• Seasoning tips: For a subtle spice kick, add a pinch of crushed red pepper flakes when adding the Worcestershire sauce.

Can I Make This French Onion Soup Ahead?

Yes, you can make this French Onion Soup ahead of time. Simply prepare the soup according to the recipe instructions, then allow it to cool completely before transferring it to an airtight container. Store it in the refrigerator for up to 3 days. When ready to serve, reheat the soup gently on the stove or in the microwave until warmed through.

Recipe Variations

• Vegan delight: Substitute the butter with olive oil and use vegan cheese and vegetable stock to turn this into a vegan-friendly dish.
• Meaty addition: Add thinly sliced cooked beef or sausage to the soup before the slow cooking phase for an extra protein boost.
• Alcohol-free version: Instead of white wine, use a mixture of white wine vinegar and water to mimic the acidity without the alcohol.
• Richer broth: For a richer broth, replace half of the stock with beef consommé, enhancing the umami flavor of the soup.
• Crunchy twist: Add a layer of caramelized onions on top of the cheese before grilling for an extra texture in each bite.

What To Serve With French Onion Soup

Serve your delicious French Onion Soup with a crusty baguette for dipping. Add a fresh green salad on the side for a refreshing contrast. Roasted garlic bread or cheesy garlic knots would also complement the soup beautifully.

You can also pair it with a creamy potato gratin or a savory herb focaccia for a more substantial meal.

How To Store Leftover French Onion Soup

In The Fridge: Transfer the soup into an airtight container once it has cooled completely. Store it in the refrigerator for up to 3 days. When ready to enjoy, simply reheat it on the stove or in the microwave until heated through.

In The Freezer: French Onion Soup can be stored in the freezer, but be cautious as the texture of the onions may change upon thawing. It’s best enjoyed fresh, but if freezing, do so in an airtight container for up to 2 months. Thaw overnight in the refrigerator before reheating.

How To Reheat Leftover French Onion Soup

Reheat your leftover French Onion Soup gently on the stove over low heat, stirring occasionally. Alternatively, microwave it in short intervals, stirring in between, until warmed through. Garnish with fresh herbs or additional cheese before serving, if desired. Enjoy the comforting flavors all over again!

Check out More Slow Cooker Recipes:

• Slow Cooker Irish Stew with Beef and Guinness
• Slow Cooker Chicken Rice Soup
• Slow Cooker Pat’s Scouse