This easy Crockpot French onion soup has rich, beefy broth filled with caramelized onions and topped with melty cheese. I love this hands-free spin on the classic recipe, made in the slow cooker!

For more cozy soup inspiration, try this creamy tortellini soup and Italian Wedding soup.

 

Easy Slow Cooker French Onion Soup

Crockpot French onion soup might be my favorite way to make this classic recipe! It’s savory and delicious, with plenty of caramelized onions cooked in a rich, beefy broth with herbs. This weeknight-friendly version leaves the work to my slow cooker, and the flavors are incredible after hours in the low and slow heat. All that’s left to do afterwards is add bread or croutons, and melt over the cheese!

Why I Love This Crockpot French Onion Soup

• Rich and savory. This soup gets its flavor from sweet, caramelized slow-cooked onions in a savory beef broth with herbs. Don’t forget the thyme! It’s the perfect pairing with all that buttery richness.
• Cheesy. Just like the classic recipe, I top my bowls with thick slices of crusty bread and heaps of melty Gruyere cheese. Too good!
• Make-ahead. This soup comes together over hours in the crockpot, and most of them are completely hands-free. I love that I can leave it to my slow cooker and come back to a cozy onion soup that’s ready to serve. Or, I’ll freeze it for future cravings!

Ingredients You’ll Need

Most of the flavor in French onion soup comes from the combination of onions caramelized in butter, with a splash of wine and fresh thyme. I’ve included some notes here. Have a scroll to the recipe card after the post for a printable ingredients list with amounts.

• Onions – The best onions for French onion soup are sweet onions, like Vidalia, which aren’t as pungent. You can use yellow onions if that’s what you have. In that case, add an extra 1/4 teaspoon of sugar to the recipe.
• Unsalted Butter – Salted butter works, too, just reduce the added salt that comes later on.
• Sugar – Granulated, brown sugar, or any kind of sugar (except powdered sugar) will work here.
• Seasonings – Fresh thyme is a must! Emphasis on fresh. It’s the signature aromatic for this soup. You’ll also need salt and pepper to taste, and a bay leaf.
• Beef Broth – I use low-sodium beef broth or stock. Chicken broth is a good alternative, though the soup won’t be quite as rich. For a vegetarian version, use vegetable stock.
• White Wine – Choose a dry white wine, like Chardonnay or Pinot Grigio. If you’d prefer to cook without it, substitute extra stock instead.
• Bread – For topping the bowls. You’ll want to use sturdy, crusty bread, like French bread. You can also top your soup with croutons.
• Gruyere cheese – The classic choice for French onion. Feel free to use Swiss cheese, or another melty cheese instead.

How to Make French Onion Soup in the Slow Cooker

This slow cooker French onion soup comes together in two stages: slow cooking the onions so that they caramelize, and then slow cooking again with wine and stock. You’ll find the printable recipe details in the recipe card below the post.

To start, dump your sliced onions into the crockpot with melted butter and sugar, and let that cook, covered, for 8 hours on LOW. You want the onions to be nicely browned and caramelized before you add the stock. Stir in the beef broth, wine, thyme, and bay leaf, and cook for another 4 hours.

How to Serve

When you’re ready to serve, ladle your slow cooker French onion soup into bowls. Top each bowl with a bread slice and load on the shredded cheese. You’ll pop that under the broiler for 2-3 minutes to get the cheese golden and melty. I like to place the bowls onto a baking sheet first. It makes it easy to transfer them to and from the oven!

Speed Things Up On the Stovetop!

If I’m pressed for time, I’ll kickstart this soup by caramelizing the onions on the stovetop first. All you do is combine the onions, butter, sugar, salt, and pepper in a large skillet, and let that cook for about 25 minutes. Add the browned onions to the slow cooker with the stock and herbs, and proceed with the recipe, cooking on LOW for 6 hours instead.

What Goes With French Onion Soup?

This crockpot French onion soup is the perfect “fancy” starter! I love to serve it with my easy rib-eye steak dinner or grilled scallops when we have guests over for dinner. Sometimes, I’ll bulk things up further with couscous and a side of caponata. This cheesy, beefy soup is also a cozy lunch served bistro-style with a Cobb salad.

Storing and Reheating Leftovers

• Refrigerate. This onion soup only gets better with time! Refrigerate the soup in an airtight container for up to 4 days. The flavors continue to mingle and the leftovers are delicious.
• Reheat. Microwave servings for 1-2 minutes, or until warm. You can also reheat this soup in a pot on the stovetop over medium heat for 5-7 minutes.
• Freeze. French onion soup freezes great. Transfer soup portions to freezer-friendly bags or containers and freeze the soup for up to 3 months. Let it thaw in the fridge overnight before serving. Reheat it as usual.

More Slow Cooker Soup Recipes

• Slow Cooker Creamy Cauliflower Soup
• Slow Cooker Vichyssoise Soup (Leek and Potato Soup)
• Crock Pot Chicken Enchilada Soup
• Slow Cooker Vegetable Soup
• Crock Pot Lemon Rice Soup