French Onion Casserole

French Onion Casserole is a comforting dish with bold, savory flavors in one rich, cheesy bake. Caramelized onions, beef broth, and Gruyère give it that deep French onion soup flavor, while pasta makes it hearty enough for a full meal. If you’re a fan of baked pasta or French onion soup, this version brings the best of both worlds.

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This casserole is one of those go-to recipes I pull out for a potluck or weeknight dinner when I want to keep things simple, or when I’ve got a few people coming over. It holds up well in the fridge, and also stores well in the freezer if you skip the toppings until you’re ready to serve. Leftovers don’t last long around here, but they reheat great when they do.

Ingredients You’ll Need

You’ll need all the ingredients shown in the photograph below.

How to Make French Onion Casserole with Step-By-Step Instructions

Scroll down for the full recipe card containing a full printable recipe and measurements in both US customary and metric units.

If you follow my simple steps, you’ll find it easy to make this cheesy, comforting onion casserole right in your own kitchen.

Caramelize the Onions

Start by melting the butter in a large pot, a large skillet, or a Dutch oven over medium heat. Add the sliced onions and stir to coat them in the butter.

Let them cook slowly, stirring occasionally, for about 20 to 25 minutes until they’re soft, deeply golden, and full of flavor. This step builds the base of your casserole, so take your time with it.

Deglaze the Onion Casserole Base

Once the onions are caramelized, stir in the salt and pour in the cooking sherry. It’ll bubble and steam—use this moment to scrape up all the browned bits stuck to the bottom of the pot.

Let it simmer for about a minute. Sprinkle in the flour and stir well to coat the onions. Cook for 2 to 3 more minutes until the mixture thickens slightly.

Add Broth and Pasta

Pour in the beef broth and bring everything to a boil. Stir in your dry pasta—something short like rotini, fusilli, or penne works great here.

Let it cook for around 10 minutes, stirring occasionally, until the pasta is just al dente. It’ll finish cooking in the broiler, so you don’t want it too soft at this stage.

Mix in Cheese and Seasoning

Once the pasta’s ready, stir in the black pepper, fresh thyme, and half of the grated Gruyère cheese. Mix well so the cheese melts into the hot mixture, giving it a creamy, savory texture.

Prepare the Topping

In a separate small bowl, combine the panko breadcrumbs and melted butter. Stir until the crumbs are evenly coated and golden.

Assemble and Broil the Casserole

Sprinkle the remaining Gruyère cheese over the top of the onion casserole, then layer on the buttery panko topping.

Place the pot (or transfer it to an oven-safe baking dish) under the broiler for 5 to 7 minutes. Watch closely—it’s ready when the top is golden brown and bubbling.

Serve Onion Casserole Warm and Fresh

Let the casserole rest for a few minutes before serving so it firms up a bit and is easier to scoop. Finish with a sprinkle of extra thyme for a fresher bite, and if you like a little herby kick. Enjoy!

Recipe Notes and Expert Tips

I’ve gathered a few helpful tips to make sure your French Onion Casserole turns out just right every time:

• Take Time with the Onions: Don’t rush the onions—slow cooking them brings out their sweet, deep flavor that gives this casserole its signature taste.
• Deglaze for Flavor: Sherry helps lift the caramelized bits from the bottom of the pot, adding a deeper flavor to the sauce.
• Go for Short Pasta: Use pasta shapes that can hold onto the sauce—penne, rotini, or fusilli work best.
• Swap in Parmesan Cheese: If you don’t have Gruyère, freshly grated Parmesan works in a pinch—it won’t be quite as creamy, but it still brings a rich, savory bite.
• Stir While Cooking Pasta: Give the pasta an occasional stir while it simmers in the broth to prevent sticking and make sure it cooks evenly.
• Don’t Walk Away from the Broiler: Keep a close eye when broiling—toppings can go from golden to burnt quickly.
• Let It Set: Resting the casserole for a few minutes before serving makes it easier to portion and gives the flavors time to settle.
• Top It Off Your Way: Feel free to add crispy fried onions or chopped parsley for extra crunch and color before serving.

How to Store Leftovers

Transfer any leftovers to an airtight container and store in the fridge for up to 3-4 days. You can reheat individual servings in the microwave, on the stovetop, or pop the whole dish in the oven until warmed through.

If you want to freeze it, do so before broiling for up to a month—just leave the cheese and breadcrumb topping off until you’re ready to reheat, as they don’t freeze very well. Thaw overnight in the fridge, then add the topping and broil just before serving for the best texture.

What to Serve With French Onion Casserole

Because this French onion casserole is rich and cheesy, it pairs best with lighter sides to keep the meal balanced. A simple green salad with vinaigrette or a side of steamed vegetables like green beans, broccoli, or asparagus works great.

You can also serve it with protein-packed options, such as grilled chicken or a couple of soft-boiled eggs, for a more filling plate. Toast or baguette slices are perfect for soaking up the sauce, and for something refreshing, a tomato and cucumber salad adds just the right contrast.

More Easy Recipes for You to Try at Home

I’ve rounded up more simple and hearty casseroles, like this one, that bring big flavor to your dinner table without a ton of prep work.

• Chicken Salad Sandwich
• Marry Me Chicken Gnocchi
• Miso Butter Chicken Thighs
• Shrimp Cauliflower Fried Rice
• Blackened Chicken Club Sandwiches

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