Slow-Cooker French Onion Soup

The French may have first invented French onion soup, but Southerners are revolutionizing this classic dish with the help of one of our favorite kitchen gadgets: the slow cooker. We'll take any chance we can get to break out our slow cookers, but after testing this recipe, we can confirm that this classic soup is even tastier (and easier than ever!) when prepared using this method.

In a soup that is simple, leaning on only a few ingredients to deliver maximum flavor, a slow-cooking method really allows time to draw out all the sweetness and richness that tender caramelized onions bring to the table. In this recipe for French onion soup, deep, rich caramelized onions get a little zing from sherry vinegar, which is then topped with bread and gooey cheese—really, what more could we ask for?

Caramelized onions are notoriously fussy and time-consuming, but this genius method seriously cuts down the hands-on work (read: no babysitting your onions on the stove). Save at least 30 minutes at the stove by using the slow-cooker to make sweet, tender onions that require (almost) no stirring. Start your onions in the morning, and enjoy the rich smell of caramelizing onions all day without all the fuss.

Ingredients for Slow-Cooker French Onion Soup

To make this incredibly flavorful soup, you'll need:

• Vidalia onions: The official state vegetable of Georgia, Vidalia onions are mild yellow onions with a slightly sweet flavor, perfect for caramelizing. If needed, you can substitute with other types of white or yellow onions.
• Unsalted butter: Adds richness and helps the onions cook and caramelize.
• Granulated sugar: Enhances the natural sweetness of the onions and boosts the caramelization.
• Kosher salt and black pepper: Seasons the onions.
• Thyme sprigs and fresh thyme leaves: Adds an herbaceous, floral note.
• Bay leaf: Adds a subtle, herbal note.
• Lower-sodium beef broth: For a rich, meaty flavor. Can be substituted with other types of broth or stock.
• Sherry vinegar: Adds a hit of acidity that balances the sweetness of the onions.
• Baguette slices: A classic topping for the soup. Can be substituted with other types of sliced breads, or croutons.
• Gruyère cheese: The cheese melts over the top of the baguette slices for a gooey, cheesy texture and rich, nutty flavor.

How To Make Slow-Cooker French Onion Soup

Full instructions are below, but here's a brief recap before you get started:

• Step 1. Stir together onions, melted butter, sugar, salt, and pepper in a 6-quart slow cooker. Top with thyme and bay leaf. Cover and cook on HIGH, stirring once halfway through, until onions are deep golden brown, 6 to 7 hours.
• Step 2. Remove thyme and bay leaf. Stir in broth and vinegar. Cover and heat through on HIGH about 30 minutes.
• Step 3. Preheat oven to broil, with rack about 6 inches from heat. Divide soup between 6 ovenproof ramekins; place on a baking sheet. Top each with 2 baguette slices and cheese. Broil until golden brown. Sprinkle with thyme and pepper. Serve immediately.

What To Serve With Slow-Cooker French Onion Soup

This soup makes a lovely starter, especially when paired with other French dishes. It's also substantial enough to act as the main event.

Serve as a first course or side dish alongside French classics like moules frites, croque monsieur, cast-iron seared steak, roasted chicken, and more. Pair with roasted vegetables or a side salad for a hearty dinner.

How Can I Serve French Onion Soup Without Ramekins?

If you don't have oven-safe ramekins on hand, broil the cheese-topped baguette slices on a baking sheet until golden and bubbly. Serve the soup family-style or portioned into bowls, topping with the hot bread right before serving.

Can I Make Slow-Cooker French Onion Soup Ahead?

Prepare this soup up to three days in advance. Cool and refrigerate, then reheat in the slow cooker or on the stovetop until hot throughout. Top with bread and broil as directed before serving. This soup can also be frozen for up to three months. Thaw in the refrigerator overnight, then reheat and serve as directed.

More Caramelized Onion Recipes You'll Love

The flavor of caramelized onions is hard to beat. We love it in dips, casseroles, mashed potatoes, quiche, and more:

• Fig Flatbread
• Caramelized Onion Dip
• Caramelized Onion, Spinach, and Pork Strata
• Turkey Grilled Cheese with Gruyere and Caramelized Onion
• Caramelized Vidalia Onion Pasta with Herbed Breadcrumbs
• Caramelized Onion-and-Mushroom Quiche
• Dairy-free Mashed Potatoes with Caramelized Vidalia Onions
  
• Croissant Breakfast Casserole

Editorial contributions by Katie Rosenhouse.