This French onion casserole recipe takes all the delicious, comforting elements of French onion soup. It turns them into a side dish you can put on a plate. Silky caramelized onions are tossed with flour and butter. This creates a rich sauce. It’s then topped with croutons and layers of melted cheese. It’s perfect next to homey braised beef or casual roast beef sliders.

Ingredients for French Onion Casserole

• Onions: A generous amount of onions are thinly sliced and cooked until very tender. You can pretty much use any type of onion here, but I always use yellow onions. When they caramelize, the yellow onions become sweet but still have a slightly pungent flavor.
• Butter: Cooking onions in butter allows them to soften and turn slightly golden, delivering luxurious flavor.
• Flour: All-purpose flour melts together with butter and broth to thicken the sauce.
• Beef broth: Store-bought or homemade broth brings the flavors of French onion soup together for this casserole.
• Sherry: This fortified wine is a secret ingredient. It adds a sweet, nutty complexity to this dish. It’s also great in other soups like split pea soup or mushroom soup. If you’d prefer not to use any alcohol, you can also use additional beef broth.
• Croutons: Salad croutons are a simple way to top this dish with bread. They hold up well to the sauce and melted cheese. Use a store-bought variety for ease, or make homemade croutons.
• Swiss cheese: Nutty shredded Swiss cheese melts beautifully. Buy a block of Swiss cheese and shred it fresh for the best flavor and meltability. Gruyere or a young Comté are good substitutes.
• Parmesan cheese: Grated Parmesan cheese doesn’t melt, but it adds a lot of flavor to the cheese topping. You can use Pecorino Romano if you prefer.

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