Slow-Cooker French Onion Soup

Stuff You Need

• 4 tablespoons unsalted butter
• 4 pounds yellow onions, halved and thinly sliced
• 2 teaspoons kosher salt, divided
• 1 tablespoon brown sugar
• 1 cup dry white wine
• 6 cups beef broth
• 2 cups chicken broth
• 4 sprigs fresh thyme
• 2 bay leaves
• 1 teaspoon black pepper, divided
• 8 ounces rustic sourdough bread, cubed
• 2 tablespoons extra-virgin olive oil
• 6 ounces Gruyère cheese, shredded
• 4 ounces Swiss cheese, shredded

Stuff to Know Before Cooking

Proper onion caramelization takes around 55 to 70 minutes.

If oven-safe bowls aren’t available, broil bread cubes topped with cheese on a baking sheet until melted, then transfer onto individual soup bowls.

Caramelize the Onions

Melt 4 tablespoons unsalted butter in a Dutch oven over medium-high heat. Add 4 pounds thinly sliced yellow onions, 1 teaspoon kosher salt, and 1 tablespoon brown sugar.

Cover and cook, stirring occasionally, until onions become translucent, about 20 minutes.

Remove lid and cook until liquid evaporates and onions begin browning, 5 to 10 minutes. Reduce heat to medium and continue cooking uncovered, stirring frequently, until onions become deeply caramelized, about 30 to 40 minutes.

Lower heat if onions begin to scorch.

Build the Soup

Add 1 cup dry white wine, scraping browned bits from the pot. Cook until nearly evaporated, about 2 minutes. Stir in 6 cups beef broth, 2 cups chicken broth, 4 sprigs thyme, 2 bay leaves, ½ teaspoon black pepper, and remaining 1 teaspoon kosher salt.

Bring to a boil over high heat, reduce heat to medium-low, and simmer uncovered for 30 minutes.

Prepare the Sourdough Croutons

Preheat oven to 350°F with rack in the middle position. Toss 8 ounces rustic sourdough cubes with 2 tablespoons olive oil, ½ teaspoon kosher salt, and remaining ½ teaspoon black pepper. Spread evenly on a rimmed baking sheet and bake until crisp and golden, 15 to 18 minutes.

Remove from oven and set aside. Increase oven temperature to 500°F.

Assemble and Bake

Discard thyme sprigs and bay leaves from the soup; season soup to taste with additional salt and pepper. Place six oven-safe crocks on a rimmed baking sheet and divide soup evenly among them.

Sprinkle half the Gruyère (3 ounces) and Swiss cheese (2 ounces) over each soup serving, then top evenly with sourdough croutons. Finish by topping with remaining cheeses.

Bake until cheese is melted and bubbling, 5 to 7 minutes. Allow to cool for about 5 minutes before serving.

Dutch Oven French Onion Soup

This French onion soup is deeply savory and rich, with caramelized onions simmered in red wine and beef broth for bold, layered flavor. Toasted baguette cubes and melted Gruyère add a cheesy, golden crust to every spoonful.

Print Pin Rate

Prep Time: 15 minutes minutes

Cook Time: 1 hour hour 50 minutes minutes

Total Time: 2 hours hours 5 minutes minutes

Ingredients

• 4 tablespoons unsalted butter
• 4 pounds yellow onions halved and thinly sliced
• 2 teaspoons kosher salt divided
• 1 tablespoon brown sugar
• 1 cup dry white wine
• 6 cups beef broth
• 2 cups chicken broth
• 4 sprigs fresh thyme
• 2 bay leaves
• 1 teaspoon black pepper divided
• 8 ounces rustic sourdough bread cubed
• 2 tablespoons extra-virgin olive oil
• 6 ounces Gruyère cheese shredded
• 4 ounces Swiss cheese shredded

Instructions

• Melt butter; cook onions with salt and brown sugar until deeply caramelized (55-70 min).
• Stir in white wine; cook briefly, then add broths, thyme, bay leaves, pepper, and salt; simmer 30 min.
• Toss sourdough cubes with olive oil, salt, pepper; bake at 350°F until crisp (15-18 min).
• Ladle soup into oven-safe bowls, top with cheeses and croutons; bake at 500°F until bubbly (5-7 min).
• Let cool 5 min before serving.