Slow Cooker French Onion Soup

Why This Slow Cooker French Onion Soup Recipe Works

• Slow simmering is the secret. French onion soup really has an amazing depth of flavor when done slowly. That’s why the slow cooker or crock pot is perfectly suited for it!
• Hands-free. With this easy method, there’s no need to hover over a pot on the stovetop for hours. The soup cooks over low and slow heat on its own, no fuss necessary.
• Make it ahead. You can prepare the soup in the slow cooker up to

What You’ll Need

This classic soup recipe requires only a few simple ingredients. I’ve covered them below. Scroll to the recipe card after the post for the printable ingredients list and recipe details.

• Yellow Onions – Yellow onions are the best choice for onion soup. They’re slightly milder than white onions, and they caramelize beautifully. I don’t recommend red onions or similar “salad” types, as they tend to be too soft.
• Butter – For sautéeing. I love the added flavor that comes with butter, but you can use olive oil if you’d prefer.
• Beef Broth – Alternatively, you can make a vegetarian soup with vegetable broth.
• Red Wine – Choose a dry red wine, like Pinot Noir or Cabernet Sauvignon. You can also use a combination of brandy or vermouth and white wine for something a little sweeter.
• Herbs – Bay leaf, and dried or fresh thyme. If you’d like to use fresh thyme, you’ll need about 3x the amount of fresh herbs as dried.
• Bouillon Cubes – Added for extra flavor.
• Worcestershire Sauce – I love including Worcestershire sauce in French onion soup for its rich umami flavor. Soy sauce works well, too.
• French Baguette – The traditional way to serve French onion soup is with a toasted bread slice placed on top with melted Gruyere cheese. For this reason, choose a crusty bread, like French bread, sourdough, or Italian ciabatta. The edges will crisp up nicely under the broiler and the bread is sturdy enough to soak up the soup without becoming mushy too quickly.
• Gruyere Cheese – Grated, also for garnish. If you can’t find Gruyere cheese, see below for suggested substitutes. I also add a parmesan cheese.

What Can I Use Instead of Gruyere Cheese in French Onion Soup?

Purists will insist that when it comes to French onion soup, it’s Gruyere cheese or bust! And I’m mostly in agreement. Gruyere cheese is smooth and melty, rich in flavor, and a match made in heaven with the broth and caramelized onions. That being said, these are the best alternative cheese options for French onion soup:

• Swiss, Emmental, or Raclette (these are the best alternatives)
• Jarlsberg
• Gouda
• Cheddar
• Provolone
• Mozzarella

How to Make French Onion Soup in the Slow Cooker

Flavor is what we’re after with onion soup, and nothing brings flavors together better than the crock pot. For this recipe, I use my Crock-Pot® since it’s such a great option for busy days and for entertaining. Plus, the flavors still come together so beautifully when cooked over low and slow heat. Here’s how to make easy French onion soup in a slow cooker:

1. Cook the onions. First, combine the onions with butter in your slow cooker. Season with salt and pepper and then cook the onions on high heat for 3-4 hours, until tender.
2. Add the rest of the ingredients. Next, you’ll add in the broth, wine, bay leaf, thyme, bouillon, and Worcestershire. Cook the soup on high for another 2-3 hours, until the onions are cooked down.
3. Garnish. When it’s time to serve, ladle the soup into oven-safe bowls (I like to use ramekins). Top each bowl with 2 slices of crusty bread and a generous pile of grated Gruyere cheese.
4. Broil. Place the soups under the broiler until the cheese is bubbling and melted.

Stovetop Method

You can also make this traditional French onion soup on the stove if you’d perfer! Perks of the stovetop method are, of course, that you can really get the onions caramelized in butter. It’s also a little quicker to whip up onion soup on the stove than in the slow cooker.

1. Sauté. Melt the butter in a large Dutch oven, add the onions, and sauté over medium heat for 10-12 minutes until the onions are browned. Season with salt and pepper to taste.
2. Combine. Pour in the broth and wine, and add the herbs, bouillon, and Worcestershire sauce. Stir, and bring the soup to a boil before lowering the heat to a simmer.
3. Cook. Simmer for 1 hour uncovered, giving the soup the occasional stir. When it’s time to serve, follow the same directions as above to add the bread and cheese before broiling.

Tips for Success

• Thicken soup that’s too thin. Flour will help to thicken soup that is too runny. If you’d like to thicken the broth a bit, sift in a small amount of flour and give it a chance to set up a bit.
• Caramelize the onions quickly. To save some time, you can brown your onions in a pan first before adding them into your slow cooker with the other ingredients. Caramelize the onions slowly to avoid burning them, until they’re tender and nicely browned.
• Don’t skip the toppings! French onion soup without bread and Gruyere cheese is like leaving the house without clothes on. No one is stopping you, but why?
• Don’t rush the process. The key to this classic soup recipe is time. Giving due respect to browning the onions, followed by the broth and onions cooking for long hours over low heat is what transforms the ingredients into a spectacular warm and cozy meal.

Serving Suggestions

Because of its hearty, rich flavors, I love to serve French onion soup next to a garden salad or veggies, like asparagus or garlicky mushrooms. And even though it comes topped with bread, I can’t resist a basket of garlic knots on the side! For a heartier meal, onion soup pairs nicely with mashed potatoes, broccoli cheese casserole or cheesy baked mashed potatoes. Cheese lovers, rejoice!

How to Store and Reheat Leftovers

I’ll put it out there: French onion soup is almost even better a day or two later, when all the flavors have had the chance to really meld together. It’s easy to store or freeze the soup (without the toppings):

• Refrigerate. Allow the soup to cool completely and then store leftover soup airtight in the fridge, where it will keep for up to 3 days.
• Freeze. Like most soups, French onion soup freezes extremely well. Make sure you freeze any leftovers without the bread and cheese, and store the soup in a freezer safe container. French onion soup will keep frozen for up to 3 months, and can be thawed overnight and then reheated on the stovetop or in the microwave.

More Cozy Soup Recipes

• Chipotle Lime Chicken Soup
• Bacon Cheeseburger Soup
• Sloppy Joe Stew
• Taco Truck Chili
• Chipotle Chicken Corn Chowder