FRENCH ONION SOUP CASSEROLE

French Onion Soup Casserole image

Provided by Erin Jeanne McDowell

Time 1h40m

Yield 8 servings

Number Of Ingredients 16

5 tablespoons unsalted butter
2 tablespoons extra-virgin olive oil
5 large or 8 medium Vidalia onions, sliced
Kosher salt and freshly ground black pepper
1 bay leaf
2 tablespoons all-purpose flour
1 cup whole milk
1/2 cup freshly grated Parmesan
Dash freshly grated nutmeg
1 tablespoon balsamic vinegar
1 tablespoon Worcestershire sauce
2 1/2 cups beef broth
1 tablespoon chopped fresh thyme leaves
1 baguette, cut into 1/2-inch-thick slices
1 1/3 cups shredded mozzarella
Chopped chives, for finishing

Steps:

In a large pot, melt 2 tablespoons of the butter over medium heat. Add the oil and onions and toss well to coat the onions. Season with salt and pepper, add the bay leaf, and continue to cook, stirring occasionally, until the onions soften, 5 to 7 minutes.
Reduce the heat to medium low and continue to cook, uncovered, stirring occasionally, until the onions begin to caramelize, 25 to 30 minutes longer.
While the onions cook, make the bechamel sauce: Melt 2 tablespoons of the remaining butter in a small saucepan over medium heat. Add the flour and whisk to combine. Whisk in the milk and bring to a simmer, whisking. When the sauce thickens, stir in the Parmesan and nutmeg. Season with salt and pepper. Set aside.
Preheat the oven to 400 degrees F. Grease a 9-by-13-inch baking dish with the remaining 1 tablespoon butter.
When the onions begin to caramelize, stir in the balsamic and Worcestershire and cook for 1 to 2 minutes more. Add the broth and thyme and bring to a simmer over medium heat. Remove and discard the bay leaf.
Transfer the onion mixture to the prepared dish. Arrange the baguette slices on top, then spoon a little bechamel sauce over each piece of bread. Top with the mozzarella. Bake until the cheese is melted and begins to brown and the filling is bubbling, 35 to 40 minutes.
Let cool for 5 to 10 minutes. Sprinkle with chives and serve.