Mushroom Lasagna with Gruyère Bechamel

To make the mushrooms, in a large fry pan over medium-high heat, melt 5 Tbs. of the butter. Working in 4 batches, add the mushrooms and cook, stirring occasionally, until tender and lightly browned, about 10 minutes per batch. Before cooking the third and fourth batches, add 5 Tbs. more butter to the pan. Transfer each batch of cooked mushrooms to a large bowl.

In the same pan over medium-high, melt the remaining 1 Tbs. butter. Add the garlic and cook, stirring occasionally, until fragrant, about 1 minute. Return all of the mushrooms to the pan, season with salt and black pepper and cook, stirring occasionally, until caramelized, about 25 minutes. Add the wine, lemon juice and thyme, stirring to scrape up the browned bits from the bottom of the pan. Remove from the heat. Transfer 1 cup (3 oz./90 g) of the mushrooms to a small bowl and reserve for garnishing the baked lasagna.

To make the bechamel, in a large fry pan over medium heat, melt the butter. Sprinkle in the flour and cook, whisking occasionally, until the mixture thickens and starts to smell toasty, 3 to 5 minutes. Whisk in the milk and cook, whisking constantly, until smooth and no lumps remain, about 2 minutes. Increase the heat to medium-high and bring to a simmer, then cook, whisking occasionally, until the mixture is velvety, about 3 minutes. Reduce the heat to medium-low and cook, whisking occasionally, until the mixture coats the back of a spoon, about 10 minutes. Remove from the heat and whisk in the Gruyère, Parmesan, lemon zest, cayenne and nutmeg. Season to taste with salt and black pepper. Let cool.

Preheat an oven to 325°F (165°C). Grease a lasagna pan with olive oil.

In a large bowl, stir together the Gruyère, mozzarella and Parmesan.

Spread a thin layer of the bechamel in the prepared baking dish. Cover with a single layer of the lasagna noodles, cutting them in half or quarters as needed to fill in the gaps and edges. Spoon about 1 cup (8 fl. oz./250 ml) of the bechamel over the noodles and spread evenly. Top with about one-fourth of the mushroom mixture and sprinkle with some of the cheese mixture. Layer the noodles, bechamel, mushrooms and cheese 3 more times, ending with a final layer of noodles and cheese. Cover the lasagna with a well-oiled piece of aluminum foil.

Place the baking dish on a baking sheet. Bake until the cheese is bubbling around the edges, about 1 hour. Remove the foil and sprinkle the lasagna with some thyme leaves and more of any of the cheeses if desired. Increase the oven temperature to 400°F (200°C) and bake until the lasagna is deep golden brown and crisp around the edges, about 15 minutes more.

Remove the lasagna from the oven. If you assembled the lasagna ahead of time, reheat the reserved mushrooms in a small fry pan before garnishing.Garnish with the reserved mushrooms, thyme sprigs, lemon zest and a few grindings of black pepper. Cut the lasagna into slices and serve. Serves 8 to 10.

Williams Sonoma Test Kitchen