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French Onion Soup Casserole
Crispy toasted baguette slices soak up a rich, sherry-infused beef broth in this hearty twist on a bistro classic. It transforms traditional French onion soup into a sliceable, deeply savory baked dish. You'll layer slowly caramelized Vidalia onions with the toasted bread, then blanket the whole thing in melted Gruyere cheese. It's a deeply comforting meal that captures all the sweet, savory, and cheesy magic of the original bowl.
Ingredients
- ¼ cup unsalted butter
- 5 medium-size Vidalia onions, thinly sliced (about 3 lb.)
- 2 tsp. kosher salt
- ½ tsp. black pepper
- 3 fresh thyme sprigs
- 2 fresh flat-leaf parsley sprigs
- 2 bay leaves
- 1 (16-oz.) baguette, thinly sliced
- ⅓ cup all-purpose flour
- 3 cups reduced-sodium beef broth
- ½ cup dry sherry
- 8 oz. Gruyère cheese, shredded (about 2 cups)
- 1 tsp. fresh thyme leaves
Instructions
- 1Preheat the oven to 350°F. Spread the thinly sliced baguette in a single layer across a baking sheet. Bake for about 12 minutes until the bread is lightly toasted, then set it aside.
- 2Melt the butter in a Dutch oven over medium-low heat, then add the sliced onions, salt, pepper, thyme sprigs, parsley sprigs, and bay leaves. Cook for about an hour, stirring often, until the onions turn a deep golden brown. Don't rush this step; slow cooking pulls out the natural sugars for that signature sweet flavor.
- 3Once the onions are caramelized, discard the herb sprigs and bay leaves. Stir the flour into the onions and cook for 2 minutes while stirring constantly.
- 4Pour in the beef broth and dry sherry. Increase the heat to high and bring the liquid to a boil. Continue boiling and stirring for 2 to 3 minutes until the mixture thickens slightly.
- 5Arrange half of the toasted baguette slices in the bottom of a 13-by-9-inch baking dish. Spoon the thickened onion mixture evenly over the bread layer. Cover the onions with the remaining toasted baguette slices.
- 6Scatter the shredded Gruyere cheese over the top layer of bread. Cover the dish tightly with aluminum foil and bake for 30 minutes. Change the oven setting to broil, remove the foil, and broil for about 3 minutes until the cheese is melted and bubbling. Garnish with fresh thyme leaves.
Notes
- Make ahead: You can caramelize the onions up to 3 days in advance and store them in an airtight container in the fridge.
- Swap: If you don't have dry sherry, dry white wine or extra beef broth works well as a substitute.
- Cheese: For the best melt, buy a block of Gruyere and shred it yourself rather than using pre-shredded cheese.