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Slow Cooker French Onion Soup Recipe

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Discover the easiest, most flavorful slow cooker French onion soup recipe! Caramelized onions, rich broth, and melted cheese make this a cozy classic.

  • Total Time: 10-12 hours, 15 minutes
  • Yield: 6 1x

Ingredients

Scale
  • 3 pounds sweet onions, thinly sliced
  • 3 tablespoons unsalted butter, melted
  • 2 teaspoons brown sugar
  • Kosher salt and freshly ground black pepper, to taste
  • 6 sprigs fresh thyme
  • 1 bay leaf
  • 6 cups beef stock
  • 1 French baguette, sliced
  • 1 cup shredded Gruyère cheese
  • 1 cup shredded Asiago cheese

Instructions

  1. Prep the onions: Slice your onions as thinly as possible. Don’t worry about making them perfect—they’ll cook down significantly in the slow cooker.
  2. Caramelize the onions: Place the onions in your slow cooker, then stir in the melted butter, brown sugar, and a teaspoon of salt. Lay the thyme sprigs and bay leaf on top. Cover and cook on high for 8-10 hours, or until the onions are deeply caramelized and browned. (Tip: I usually start this at night so I wake up to beautifully caramelized onions by morning!)
  3. Add the beef stock: Remove the thyme sprigs and bay leaf, then pour in the beef stock. Season with salt and pepper to taste. Cover and cook on high for another 2-3 hours, until the flavors are well-blended and the soup is hot.
  4. Toast the baguette slices: Preheat your oven to broil. Place the baguette slices on a baking sheet and broil until golden brown on both sides, about 1-2 minutes per side. Watch them closely—they can burn quickly!
  5. Assemble and broil: Ladle the soup into oven-safe bowls. Top each bowl with a few baguette slices, then sprinkle generously with the shredded Gruyère and Asiago. Place the bowls on a baking sheet and broil for about 2 minutes, or until the cheese is melted and bubbly.
  6. Serve immediately: Carefully remove the hot bowls from the oven and serve right away. The soup is best enjoyed while the cheese is still melty and the baguette is crisp.

Notes

To serve your French onion soup, place each bowl on a small plate to make handling easier (since they’ll be hot from the broiler). For garnish, sprinkle a few fresh thyme leaves on top or add a crack of black pepper. A simple green salad on the side balances out the richness of the soup. You could also pair it with a small charcuterie board or some olives for a complete French-inspired meal.

  • Author: Lily
  • Prep Time: 15 minutes
  • Cook Time: 10-12 hours
  • Category: Dinner

Find it online: https://savoryrecipe.com/slow-cooker-french-onion-soup-recipe/