If you adore the rich, caramelized flavors of classic French onion soup but crave an effortlessly shareable dish, this French Onion Soup Casserole Recipe is exactly what you need. Imagine layers of toasted baguette soaked in deeply savory, slow-cooked onions and savory broth, all topped with bubbling, golden Gruyere cheese. This casserole transforms the beloved soup into a comforting, crowd-pleasing meal that’s perfect for cozy dinners or impressing your guests. It’s a dish that truly feels like a warm hug served in a bowl!
Ingredients You’ll Need
Gathering simple, quality ingredients is the secret to nailing this recipe. Each component plays a crucial role in developing the casserole’s deep flavor, vibrant color, and satisfying texture. From sweet Vidalia onions to nutty Gruyere cheese, every bite bursts with classic French onion goodness.
- 16 oz. baguette (cut into ¼-inch slices): Provides the crisp, toasty base that soaks up all the wonderful onion broth.
- ¼ cup unsalted butter (½ stick): Essential for perfectly caramelizing the onions to a luscious golden brown.
- 2 Vidalia onions (halved and sliced): Adds natural sweetness and buttery texture for the onion base.
- 3 yellow onions (halved and sliced): Gives depth and that signature French onion soup flavor.
- 1 tsp kosher salt: Enhances all the savory notes throughout the casserole.
- ½ tsp freshly ground black pepper: Adds a gentle kick for balanced heat.
- 5 fresh thyme sprigs (leaves removed): Infuses an herbal earthiness that elevates the dish.
- 1 bay leaf: Adds subtle aromatic complexity during cooking.
- ½ cup dry sherry: Boosts richness with a touch of acidity and sweetness.
- 1 cup unsalted beef broth: Brings robust, meaty flavor to the broth base.
- 2 cups unsalted chicken broth: Provides a lighter broth balance that complements the beef.
- 8 oz. freshly shredded Gruyere cheese (about 2 cups): Creates a nutty, melty topping that’s simply irresistible when browned.
How to Make French Onion Soup Casserole Recipe
Step 1: Prepare and Toast the Bread
First things first, preheat your oven to 400°F and set the rack low in the oven for even baking. Arrange the baguette slices on a metal rack atop a baking sheet and toast them until they’re a gorgeous golden brown—this crispness is what will soak up all the delicious onion broth later without turning mushy.
Step 2: Start Caramelizing the Onions
In a large Dutch oven sprayed with nonstick cooking spray, add butter, sliced onions, salt, pepper, fresh thyme leaves, and a bay leaf. Cover tightly and slow-cook the onions in the oven for one hour, allowing the butter and seasonings to gently coax out their sweetness and soften perfectly.
Step 3: Deepen the Onion Flavor
After the first hour, remove the pot and stir well, scraping the fond from the sides and bottom. Return it to the oven with the lid slightly ajar and cook for another hour, then repeat stirring. If you want more color or a deeper caramelization, cook an extra 30 minutes uncovered to get those rich golden hues that are signature to French onion flavor.
Step 4: Make the Broth Mixture
Moving the pot to the stovetop, carefully handle the hot Dutch oven using oven mitts. Remove and discard the bay leaf, then pour in the dry sherry, beef broth, and chicken broth. Bring the mixture to a steady boil while stirring to get everything incorporated and the broth slightly thickened—this takes about 4 to 5 minutes.
Step 5: Assemble the Casserole
Layer half the toasted baguette slices on the bottom of your prepared 9×13-inch baking dish. Spoon the luscious onion mixture evenly over the bread, then top with the remaining toasted slices. These layers will soak up that broth perfectly while baking.
Step 6: Add Cheese and Bake
Sprinkle a generous amount of freshly shredded Gruyere cheese on top and cover the dish with foil. Bake at 400°F for 30 minutes, allowing the cheese to melt and the casserole to heat through beautifully.
Step 7: Broil for a Perfect Finish
Remove the foil and set your oven to broil. Broil the casserole for about 3 minutes or until the cheese bubbles and develops a gorgeous golden crust—make sure to watch closely so it doesn’t burn!
How to Serve French Onion Soup Casserole Recipe
Garnishes
A sprinkle of fresh thyme leaves adds a lovely herbaceous pop that complements the rich onion flavors perfectly. You can also add a pinch of cracked black pepper or a drizzle of extra virgin olive oil for a subtle finishing touch.
Side Dishes
This casserole pairs wonderfully with a crisp green salad tossed in a light vinaigrette to cut through the richness. Roasted root vegetables or steamed green beans also make excellent side dishes that keep the meal balanced and hearty.
Creative Ways to Present
Try serving the casserole in individual ramekins for charming, personalized portions that feel extra special. Or layer it in clear glass casseroles so guests can admire the beautiful layers of toasted bread, onions, and melted cheese before digging in.
Make Ahead and Storage
Storing Leftovers
Once cooled, cover the casserole tightly with foil or plastic wrap and refrigerate. It keeps well for up to 3 days without losing any of its delicious flavor or texture, making it a fantastic recipe for leftovers or weekday meals.
Freezing
This French Onion Soup Casserole Recipe freezes beautifully! Assemble but don’t bake, then wrap tightly and freeze for up to 2 months. When ready to enjoy, thaw overnight in the refrigerator and bake as directed for a freshly baked taste.
Reheating
To reheat leftovers, cover the casserole with foil and warm in a 350°F oven until heated through, about 20-25 minutes. Remove the foil in the last 5 minutes to revive that bubbly cheese crust just like the original bake.
FAQs
Can I use a different type of bread?
Absolutely! While a baguette offers the perfect balance of crispness and softness, crusty sourdough or ciabatta can also be great alternatives. Just be sure to slice and toast them well so the bread holds up in the casserole.
Can this recipe be made vegetarian?
Yes! Simply replace the beef broth with a rich vegetable broth and maintain the chicken broth or use vegetable broth all around. The sherry and caramelized onions will still provide fantastic flavor depth.
Is Gruyere cheese mandatory?
Gruyere is the classic choice for its nutty, melty texture, but Swiss cheese or even a mild cheddar can work nicely if you want a slightly different flavor profile or if Gruyere is hard to find.
How long does it take to caramelize the onions?
In this recipe, slow-cooking the onions in the oven takes around 2.5 hours total, including stirring intervals. This method allows even caramel cooking without burning and highlights the sweet, rich flavors perfectly.
Can I make this recipe gluten-free?
Yes, just swap the baguette for your favorite gluten-free bread and follow the recipe as usual. Toasting the bread slices is still key to ensure they absorb the broth well without becoming soggy.
Final Thoughts
This French Onion Soup Casserole Recipe is a delightful twist on a timeless classic, turning the beloved soup into an easy-to-share family favorite. Its rich flavors, gooey cheese, and crusty bread layers come together to create pure comfort with every forkful. I can’t wait for you to make it and enjoy the same warm, cozy moments it brings every time I do!
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French Onion Soup Casserole Recipe
- Prep Time: 10 minutes
- Cook Time: 3 hours 15 minutes
- Total Time: 3 hours 25 minutes
- Yield: 6 servings (6 bowls)
- Category: Casserole
- Method: Baking
- Cuisine: French
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
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.
