Description
This French Onion Soup Casserole transforms the classic soup into a comforting, layered casserole perfect for family dinners. Toasted baguette slices are nestled between slowly caramelized onions cooked with fresh thyme and finished with a savory blend of beef and chicken broth, topped generously with melted Gruyere cheese baked to a golden, bubbly perfection.
Ingredients
Scale
Bread
- 16 oz. baguette (cut into ¼-inch slices, about 1 loaf)
Onion Mixture
- ¼ cup unsalted butter (½ stick)
- 2 Vidalia onions (halved and cut top-to-bottom into ¼-inch slices)
- 3 yellow onions (halved and cut top-to-bottom into ¼-inch slices)
- 1 tsp kosher salt
- ½ tsp freshly ground black pepper
- 5 fresh thyme sprigs (leaves removed)
- 1 bay leaf
- ½ cup dry sherry
- 1 cup unsalted beef broth
- 2 cups unsalted chicken broth
Topping
- 8 oz. freshly shredded Gruyere cheese (about 2 cups)
Instructions
- Preheat Oven and Prepare Dish: Preheat your oven to 400°F and place the oven rack in the lower-middle position. Spray a 9×13-inch baking dish with nonstick cooking spray and set it aside for layering later.
- Toast Bread Slices: Arrange the sliced baguette on a metal rack set inside a baking sheet. Bake for 8-10 minutes until the bread becomes golden and slightly crisp. Remove from the oven and keep aside until needed.
- Prepare Dutch Oven for Onions: While the bread toasts, spray a large Dutch oven generously with nonstick cooking spray and ensure the onions are sliced as directed.
- Add Onions and Seasonings: Add the butter, sliced onions, kosher salt, freshly ground black pepper, thyme leaves, and bay leaf into the Dutch oven.
- First Cooking Stage of Onions: Once the baguette is toasted, cover the Dutch oven tightly and place it in the oven to cook the onions for 1 hour. Afterward, remove the pot carefully and stir well, scraping the sides and bottom to prevent sticking.
- Second Cooking Stage: Return the Dutch oven to the oven, this time with the lid slightly ajar, and continue cooking the onions for another hour to deepen their flavor.
- Final Onion Color and Texture Check: Remove the pot and stir the onions again, scraping the pot thoroughly. The onions should be soft with a rich golden-brown color. If they need more caramelization, continue cooking uncovered for an additional 30 minutes.
- Heat Onions on Stovetop: Transfer the Dutch oven to the stovetop and set heat to medium-high, remembering to use oven mitts because the pot is hot.
- Remove Bay Leaf: Take out and discard the bay leaf from the onion mixture.
- Add Liquids and Thicken: Stir in dry sherry, beef broth, and chicken broth into the onions. Bring this mixture to a boil over medium-high heat, stirring constantly, and cook until it thickens slightly, about 4-5 minutes.
- Layer Bread in Casserole Dish: Place half of the toasted baguette slices evenly on the bottom of the prepared casserole dish.
- Add Onion Mixture and Remaining Bread: Spoon the cooked onion mixture evenly over the bread layer, then top with the remaining baguette slices.
- Add Cheese and Cover: Sprinkle the shredded Gruyere cheese evenly over the top bread layer and cover the casserole dish tightly with foil.
- Bake the Casserole: Bake in the preheated oven at 400°F for 30 minutes to melt the cheese and allow flavors to meld.
- Broil for Cheese Finish: Set the oven to broil, remove the foil carefully, and broil the casserole for about 3 minutes or until the cheese is bubbly and golden. Watch closely to prevent burning.
- Garnish and Serve: Optionally garnish with additional fresh thyme leaves for a fragrant finish. Serve hot.
Notes
- Be careful when handling the hot Dutch oven during stovetop steps—use mitts to avoid burns.
- Adjust the onion caramelization time to your preference; more time will deepen the sweetness and color.
- Dry sherry adds a subtle complexity, but it can be omitted or replaced with a dry white wine if preferred.
- Gruyere cheese provides excellent melt and flavor; substitute with Swiss or Emmental if unavailable.
- This casserole is excellent for making ahead; assemble it and refrigerate before baking.
