French Onion Soup Casserole

French Onion Soup Casserole is a delightful and comforting dish that combines the rich, savory flavors of traditional French onion soup with the hearty, satisfying structure of a casserole. This dish typically begins with a generous amount of thinly sliced onions. These onions are slowly caramelized over low heat, a process that can take upwards of an hour. The slow cooking allows the natural sugars in the onions to develop, resulting in a deep golden color and a complex, sweet, and savory flavor profile.

Once caramelized, the onions are usually deglazed with a splash of a rich beverage, often a good quality beef broth or sometimes a combination of wine and broth, adding another layer of depth to the flavor. This liquid not only lifts the caramelized bits off the bottom of the pan for more flavor but also begins to form the base of the soup aspect of the dish.

Herbs like thyme and bay leaves are added for their aromatic qualities. Some recipes also include a bit of garlic for an extra punch of flavor. The mixture is then allowed to simmer, melding the flavors together beautifully.

For the casserole component, slices of crusty French bread or baguette are toasted until just crisp. These act as a base or a topping (depending on the recipe) for the casserole, absorbing the flavorful onion and broth mixture and providing a textural contrast.

The hallmark of any good French onion soup, and thus this casserole, is the generous topping of cheese. Gruyere is a popular choice for its excellent melting qualities and nutty, slightly sweet flavor, which complements the onions perfectly. The cheese is liberally layered over the top of the casserole and then broiled until it’s bubbling and golden brown, with some crispy, almost burnt edges that add a delightful crunch.

The casserole is baked until everything is heated through and the flavors have had a chance to meld together. The result is a rich, gooey, and incredibly flavorful dish that’s both comforting and sophisticated. Each bite offers the sweet and savory taste of caramelized onions, the heartiness of the bread, and the creamy, indulgent pull of melted cheese, making it a perfect dish for a cozy night in or for impressing guests at a dinner party.


3 tablespoons unsalted butter

3 large sweet onions, thinly sliced

2 cloves garlic, minced

Salt and pepper to taste

1 teaspoon thyme (fresh or dried)

2 tablespoons 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


Preheat the oven to 400°F (200°C). Spray a 9×13 inch baking dish with cooking spray.

Melt butter in a large pan over medium heat. Add onions and cook until soft, sweet, and golden brown (about 15 minutes). Add garlic, salt, pepper, and thyme; cook for 1 more minute.

Sprinkle flour over the onions, cook for a couple of minutes, then pour in the wine. Let it simmer until the liquid reduces slightly. Add both broths and bring to a simmer for 10 minutes.

Pour half the onion mixture into the baking dish. Layer half the toasted bread slices, then sprinkle with half of the Gruyère and Parmesan. Repeat with the remaining ingredients.

Bake uncovered for 20-25 minutes, or until the cheese is bubbly and browned at the edges.

Let it rest for a few minutes, then garnish with fresh parsley before serving.

Variations & Tips:

For a vegetarian version, replace the beef broth with chicken or vegetable broth.

Experiment with different cheeses for new flavors.

Use gluten-free bread for a gluten-free casserole.

Prep the casserole a day ahead and refrigerate until ready to bake.

Short on time? Use store-bought caramelized onions.

This French Onion Soup Casserole is not just a meal; it’s an experience. A perfect blend of tradition and modernity, it’s sure to be a hit at your dinner table. Enjoy the cooking, and savor the delicious moments!

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