There’s something truly magical about French onion soup. It’s one of those dishes that brings me right back to cold winter nights growing up. I remember my mom making a big pot of it, the scent of slowly caramelizing onions filling the house with warmth and comfort. But as much as I loved that classic soup, I found myself wanting to turn it into something more substantial, something that could feed a hungry family on a weeknight but still maintain that same rich, cozy flavor. That’s when I discovered this French Onion Soup Casserole.
The inspiration came during a trip to France with my best friend. We were traveling through the countryside and stopped at a small café, known for its rustic, home-style cooking. We ordered a French onion soup, and while it was as delicious as I remembered, it came served with a thick slice of toasted bread underneath the broth—almost like a casserole. That bite of soup-soaked bread and gooey Gruyère cheese was one I’ll never forget. When I got back home, I knew I had to recreate that experience but in a form that was more shareable, easy to serve, and perfect for family dinners.
This casserole version hits all the right notes—savory, cheesy, and deeply comforting. The slow-cooked onions are the star, their rich sweetness balanced by the bite of sherry and thyme. The toasted baguette slices absorb the flavorful broth, creating a hearty base, while the Gruyère cheese melts into a golden, bubbly topping. It’s the perfect marriage of soup and casserole, making it a dish that’s both nostalgic and innovative.
It’s also become a family favorite around the holidays. I can’t count how many times I’ve served it at gatherings, and it’s always a hit. The best part? It fills the house with that same irresistible aroma of onions caramelizing away in the oven—just like when my mom used to make her famous French onion soup. Every time I make it, it feels like a warm hug from the past, with a little bit of French flair.
Making French Onion Soup Casserole
Ingredients
- 16 oz loaf of baguette, sliced into ¼-inch pieces
- ¼ cup unsalted butter (half a stick)
- 3 yellow onions, thinly sliced
- 2 Vidalia onions, thinly sliced
- 1 tsp kosher salt
- ½ tsp freshly ground black pepper
- 5 sprigs fresh thyme (leaves only)
- 1 bay leaf
- ½ cup dry sherry
- 1 cup unsalted beef broth
- 2 cups unsalted chicken broth
- 8 oz Gruyère cheese, shredded (about 2 cups)
Directions
- Preheat your oven to 400°F and lightly grease a 9×13-inch baking dish with nonstick spray.
- Lay the baguette slices on a baking sheet and toast them in the oven for 8-10 minutes until golden brown and crisp. Set them aside.
- In a large Dutch oven, melt the butter over medium heat. Add the sliced onions, kosher salt, black pepper, thyme leaves, and bay leaf. Cover the pot and transfer it to the preheated oven.
- Let the onions cook for 1 hour, then remove the pot and stir well, ensuring you scrape the bottom and sides to prevent sticking.
- Return the pot to the oven, leaving the lid slightly ajar. Cook for another hour, stirring once more. If the onions aren’t caramelized yet, cook for an additional 30 minutes until they reach a deep golden color.
- Remove the pot from the oven and place it on the stovetop over medium-high heat. Discard the bay leaf.
- Add the sherry, beef broth, and chicken broth, stirring constantly as the mixture comes to a boil. Cook until slightly thickened, around 4-5 minutes.
- In your prepared casserole dish, layer half of the toasted bread slices. Pour the onion mixture over the bread and add the remaining baguette slices on top.
- Generously sprinkle the shredded Gruyère cheese over the casserole. Cover the dish with foil.
- Bake at 400°F for 30 minutes. Afterward, remove the foil and set the oven to broil. Broil for 3 minutes or until the cheese is bubbly and golden brown. Be sure to watch it closely to prevent burning.
- Garnish with additional thyme leaves before serving, if desired. Enjoy your rich, comforting casserole!
Storing Suggestion
Once the casserole has cooled, store leftovers in an airtight container in the refrigerator for up to 3 days. Reheat in the oven at 350°F until warmed through, or microwave individual servings for a quicker option.
Cooking Tips
For a richer flavor, try using caramelized onions instead of regular sautéed onions. Additionally, you can substitute the dry sherry with white wine or omit it entirely for a lighter dish.
Serving Suggestions
This French onion soup casserole pairs beautifully with a crisp green salad and a light vinaigrette. You can also serve it alongside roasted vegetables or a simple charcuterie board for a complete meal.
Ingredient Substitutions
If Gruyère cheese isn’t available, you can substitute it with Swiss cheese or a combination of Parmesan and mozzarella for a different flavor profile.
Seasonal Variations
During the fall, consider adding sautéed mushrooms or roasted garlic to the onion mixture for a heartier dish. In the spring, add fresh herbs like chives or parsley for a burst of freshness.
Allergen Information
This recipe contains dairy and gluten. To make it gluten-free, use a gluten-free baguette. For a dairy-free option, replace the butter and cheese with vegan alternatives.
FAQ:
Can I make this casserole ahead of time?
Yes, you can prepare the casserole in advance. Assemble it up to the point of adding the cheese, then cover and refrigerate. When you’re ready to bake, top it with the cheese and follow the baking instructions.
Can I freeze French onion soup casserole?
Yes, this casserole freezes well. Store it in an airtight container and freeze for up to 2 months. Thaw in the refrigerator before reheating in the oven.
How can I make this dish vegetarian?
To make it vegetarian, substitute the beef and chicken broth with vegetable broth.
What type of onions are best for this recipe?
A mix of yellow and Vidalia onions works best for a balanced flavor. Vidalia onions add a bit of sweetness, while yellow onions bring depth.
Can I use pre-shredded cheese?
While you can use pre-shredded cheese, it’s recommended to shred your own Gruyère for better melting and texture, as pre-shredded varieties often contain additives that affect melting.
How do I prevent the onions from burning while caramelizing?
Be sure to stir the onions occasionally while they cook and scrape the sides and bottom of the pot to prevent them from sticking and burning. If they cook too quickly, reduce the heat slightly.
French Onion Soup Casserole
Ingredients
- 16 oz loaf of baguette sliced into ¼-inch pieces
- ¼ cup unsalted butter half a stick
- 3 yellow onions thinly sliced
- 2 Vidalia onions thinly sliced
- 1 tsp kosher salt
- ½ tsp black pepper freshly ground
- 5 sprigs fresh thyme leaves only
- 1 bay leaf
- ½ cup dry sherry
- 1 cup beef broth unsalted
- 2 cups chicken broth unsalted
- 8 oz Gruyère cheese shredded, about 2 cups
Instructions
- Preheat your oven to 400°F. Prepare a 9x13-inch baking dish by coating it with nonstick spray.
- Place the baguette slices on a baking sheet and toast for 8-10 minutes until golden and crispy. Set aside.
- In a large Dutch oven, melt the butter and add the sliced onions, salt, pepper, thyme leaves, and bay leaf. Cover the pot and place it in the oven. Cook the onions for 1 hour, then remove the pot and stir, making sure to scrape the bottom and sides.
- Return the pot to the oven, leaving the lid slightly open, and cook for another hour. Stir the onions again, and if they are not yet caramelized, cook for an additional 30 minutes.
- Once the onions are a deep golden brown, transfer the pot to the stove over medium-high heat. Carefully remove the bay leaf.
- Pour in the sherry, beef broth, and chicken broth, stirring constantly until it comes to a boil and slightly thickens, about 4-5 minutes.
- Layer half of the toasted bread in the casserole dish, spread the onion mixture evenly over the top, and add the remaining bread slices. Sprinkle the shredded Gruyère cheese on top and cover with foil.
- Bake at 400°F for 30 minutes. Then, remove the foil and switch the oven to broil. Broil for 3 minutes until the cheese is bubbly and golden. Keep an eye on it!
- Garnish with extra thyme leaves before serving, if you like. Enjoy!
