Hey there, friends! I’m so excited to share a dish that’s been turning heads and making hearts flutter—French Onion Soup Casserole! This recipe takes the timeless, beloved flavors of French onion soup and transforms them into a hearty, cheesy casserole. Imagine everything you love about the classic soup—the rich, caramelized onions, the savory broth, and the gooey, golden cheese—but in a cozy, bake-and-serve format. It’s comfort food, amplified.
Why am I so jazzed about this one? It’s like your favorite soup decided to get cozy, and turned into a casserole—comfort on a plate. The origins of French Onion Soup are as rich as its flavor, with tales tracing back to Roman times, but this twist is as modern as it gets. Perfect for those chilly evenings or when you want to wow your dinner guests without slaving away in the kitchen all day. It’s a classic turned casserole that’s guaranteed to hug your soul with each bite!
Why You’ll Love This French Onion Soup Casserole
All the Flavor, Less Fuss: You get the deep, comforting flavors of French onion soup without the constant stovetop stirring.
Cheese Lovers’ Dream: Packed with gooey Gruyère and Parmesan cheese, this dish gives you that perfectly melted, bubbly cheese crust in every single bite.
Perfect Make-Ahead Meal: Prepare it the night before, and bake it just before serving—ideal for dinner parties or busy weeknights.
Customizable: Easily adaptable for vegetarians or those avoiding gluten. Plus, you can experiment with different cheeses to make it uniquely yours.
Crowd-Pleaser: This casserole is a hit with both kids and adults—perfect for family dinners, potlucks, or holiday gatherings.
Ingredients
3 tablespoons unsalted butter: For sautéing and caramelizing the onions.
3 large sweet onions, thinly sliced: Sweet onions add a natural sweetness and depth of flavor that’s essential to this dish.
2 cloves garlic, minced: Brings a warm, aromatic undertone.
Salt and pepper, to taste: Balances and enhances all the flavors.
1 teaspoon thyme, fresh or dried: Adds a fragrant, earthy note that complements the onions beautifully.
2 tablespoons all-purpose flour: Helps thicken the broth, giving the casserole a creamy, rich texture.
1/2 cup dry white wine: A splash of wine adds acidity and complexity; use a variety you’d enjoy drinking.
2 cups beef broth: Adds a deep, savory backbone to the dish.
1 cup chicken broth: Lightens the base and adds more dimension.
6 slices day-old French bread or baguette, toasted: Sturdy, slightly stale bread is perfect for soaking up all that delicious broth without getting too mushy.
1 1/2 cups grated Gruyère cheese: Known for its nutty, slightly salty flavor and excellent melting properties.
1/2 cup grated Parmesan cheese: Adds a sharp, salty bite that balances the richness of the Gruyère.
1/4 cup fresh parsley, chopped: Optional garnish for a pop of color and freshness.
Cooking spray: To prevent sticking and ensure easy serving.
Ingredient Tips
Onions: Opt for sweet onions (like Vidalia) for a milder, sweeter flavor, or use yellow onions for a more robust taste. Caramelizing them slowly over medium heat is key to achieving that signature depth of flavor.
Wine Substitute: If you prefer to skip the wine, simply replace it with an extra 1/2 cup of chicken or beef broth.
Broth Choices: Beef broth gives a deep, rich flavor reminiscent of classic French onion soup. For a lighter taste, increase the chicken broth or substitute with vegetable broth.
Cheese Options: While Gruyère is classic, Emmental, Swiss, or even a good sharp cheddar can also work. Mozzarella will provide a mild flavor with great melting qualities.
Bread: Using day-old bread is ideal for this casserole as it will soak up the flavors without becoming too soggy. Sourdough, ciabatta, or even a good whole grain bread can be great substitutes.
Instructions
Preheat the Oven: Set your oven to 400°F (200°C). Prepare a 9×13-inch baking dish by spraying it with cooking spray to prevent sticking.
Caramelize the Onions: In a large skillet over medium heat, melt the butter. Add the thinly sliced onions and cook, stirring occasionally, until they are soft, golden, and caramelized, about 15 minutes. This step is crucial for building flavor, so be patient! Stir in the minced garlic, salt, pepper, and thyme, cooking for an additional minute until fragrant.
Thicken the Base: Sprinkle the flour over the onions and cook for 2-3 minutes to remove the raw flour taste, stirring constantly. Slowly pour in the dry white wine, allowing it to simmer until the liquid has reduced by half.
Create the Sauce: Add the beef broth and chicken broth, stirring well to combine. Bring the mixture to a simmer and let it cook for another 10 minutes, allowing the flavors to meld together and the sauce to thicken slightly.
Assemble the Casserole: Pour half of the onion mixture into the prepared baking dish. Layer half of the toasted bread slices on top, followed by a generous sprinkle of half of the Gruyère and Parmesan cheeses. Repeat the layers with the remaining ingredients.
Bake to Perfection: Place the casserole dish in the preheated oven and bake, uncovered, for 20-25 minutes or until the cheese is bubbly and beginning to brown around the edges.
Rest and Garnish: Allow the casserole to rest for 5 minutes before serving to help it set. Sprinkle with fresh parsley for a pop of color and added freshness.
Serving Suggestions
Pair with Fresh Sides: A simple arugula salad with a lemon vinaigrette, or steamed green beans with a squeeze of lemon, adds a bright, refreshing contrast to the rich casserole.
Add a Crunchy Bread: Serve with crusty garlic bread for scooping up every bit of the cheesy, oniony goodness.
Wine Pairing: This dish pairs beautifully with a crisp white wine, like Sauvignon Blanc, or a light red, like Pinot Noir, which balances the richness with acidity.
Storage and Meal Prep Tips
Refrigerate Leftovers: Store leftovers in an airtight container in the refrigerator for up to 3 days. Reheat in the oven or microwave until warmed through.
Freeze for Later: To freeze, assemble the casserole and cover it tightly with aluminum foil before baking. It will keep in the freezer for up to 2 months. Thaw overnight in the fridge before baking as directed.
Make Ahead: Prepare the entire casserole up to 24 hours in advance, cover, and refrigerate. When ready to serve, bake directly from the fridge, adding a few extra minutes to the cooking time if needed.
Variations
Vegetarian Version: Replace the beef broth with vegetable broth and add some sliced mushrooms for a meaty texture without the meat.
Cheese Swap: Experiment with different cheeses, such as a mix of mozzarella for its stretch and cheddar for its sharpness.
Gluten-Free: Substitute gluten-free bread for the French bread or baguette to make this casserole gluten-free without compromising on taste.
Quick Prep: Use pre-caramelized onions (available in many grocery stores) to save time without sacrificing flavor.
Final Note
This French Onion Soup Casserole is a game-changer, capturing all the best parts of the classic soup in a format that’s easy to prepare and serve. It’s warm, cozy, and just what you need for those nights when you want a little extra comfort. Perfect for dinner parties, family gatherings, or just a weeknight treat!
Go ahead, give this recipe a try—you’ll find yourself coming back for seconds!
French Onion Soup Casserole
Ingredients
- 3 tbsp unsalted butter
- 3 large sweet onions thinly sliced
- 2 cloves garlic minced
- Salt and pepper to taste
- 1 tsp thyme fresh or dried
- 2 tbsp all-purpose flour
- 1/2 cup dry white wine
- 2 cups beef broth
- 1 cup chicken broth
- 6 slices day-old French bread or baguette toasted
- 1 1/2 cups grated Gruyère cheese
- 1/2 cup grated Parmesan cheese
- 1/4 cup fresh parsley chopped (for garnish)
- Cooking spray
Instructions
- Preheat oven to 400°F (200°C). Spray a 9x13 inch baking dish with cooking spray.
- Melt butter in a large pan over medium heat. Add onions and cook, stirring occasionally, until soft and golden brown, about 15 minutes. Add garlic, salt, pepper, and thyme; cook for 1 minute.
- Stir in flour and cook for 2 minutes. Pour in the wine and simmer until reduced slightly. Add beef and chicken broths; simmer for 10 minutes.
- Pour half of the onion mixture into the prepared dish. Layer half of the toasted bread on top, then sprinkle with half of both cheeses. Repeat layers with remaining ingredients.
- Bake uncovered for 20-25 minutes, or until cheese is bubbly and golden.
- Let it sit for a few minutes to set. Garnish with fresh parsley before serving.
Notes
- Swap beef broth with chicken or veggie broth for a different flavor.
- Experiment with cheeses like sharp cheddar or mozzarella.
- Use gluten-free bread for a gluten-free option.
- Prep ahead and bake when ready. For a time-saver, use store-bought caramelized onions.