This French onion casserole recipe takes all the delicious, comforting elements of French onion soup and turns them into a side dish you can put on a plate, perfect next to homey braised beef or casual roast beef sliders.
Silky, caramelized onions are tossed with flour and butter to make a rich sauce, then topped with croutons and layers of melted cheese.
Ingredients for French Onion Casserole
- Onions: A generous amount of onions are sliced thin and cooked until very tender.
- Butter: Cooking onions in butter allows them to become soft and slightly golden, and delivers luxurious flavor.
- Flour: All-purpose flour melts together with butter and broth to thicken the sauce.
- Beef broth: Store-bought or homemade beef broth brings the flavors of French onion soup together for this casserole.
- Sherry: This fortified wine is a secret ingredient that adds a sweet, nutty complexity to this dish, and 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, and they hold up well to the sauce and melted cheese.
- Swiss cheese: Nutty, shredded Swiss cheese melts beautifully (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.
Directions
Step 1: Cook the onions and make the sauce
In a large ovenproof skillet (cast iron is a great choice), melt 3 tablespoons of butter and saute the onions until tender and lightly golden brown. Stir in the flour and pepper until the onions are well coated, then gradually add the broth and sherry. Bring to a boil, then cook, stirring, until thickened, about two minutes.
Step 2: Top with croutons and cheese
In a microwave, melt the remaining 2 tablespoons of butter, then add the croutons, tossing to coat. Distribute the croutons evenly over the onion mixture, and top with cheese.
Step 3: Broil the casserole
Broil the casserole 3 to 4 inches from the heat until the cheese is melted and bubbly, one to two minutes.
French Onion Casserole Variations
- Top with fresh herbs:Â Minced fresh parsley, chives, thyme or a combination would add a bit of fresh green to this rich casserole and complement the onion flavor. Sprinkle them on after broiling.
- Add mushrooms:Â Sliced mushrooms, sauteed with the onions, would add even more flavor and depth to this delicious dish.
- Swap out croutons for dried bread:Â If you don’t have croutons, toasted baguette slices or cubed, dried bread (try a dark rye) would also work.
How to Store French Onion Casserole
Leftover French onion casserole can be stored covered in the refrigerator for three to four days.
Can you make French onion casserole ahead of time?
To make this casserole ahead of time, cook the onions with the flour and broth. This can be refrigerated for one to two days. When you’re ready to cook, gently reheat this in the skillet and top with the prepared croutons and cheese. Broil as directed.
French Onion Casserole Tips
Can I add meat to French onion casserole?
If you’d like to add protein to this dish, cook 1 pound of ground beef first, then drain it and set it aside. Stir it into the onion mixture after cooking, then top as directed.
How do I make French onion casserole vegetarian?
If you’d like to make this dish vegetarian, trade the butter for olive oil and swap the beef broth for mushroom broth.
What are the best types of onions to use in French onion casserole?
Yellow onions will cook up sweet, with an onion flavor that is just assertive enough to shine through the croutons and cheese.
