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slow cooker French onion soup

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.
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Prep Time: 15 minutes
Cook Time: 1 hour 50 minutes
Total Time: 2 hours 5 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.