Step 1

Preheat the oven to 375 degrees F.

Step 2

Bring a large pot of water to a boil with 1 tablespoon salt and a splash of oil. Add the lasagna noodles and cook for 10 minutes, stirring occasionally. Drain and set aside.

Step 3

For the white sauce, bring the milk to a simmer in a saucepan. Set aside. Melt 8 tablespoons (1 stick) of the butter in a large saucepan. Add the flour and cook for 1 minute over low heat, stirring constantly with a wooden spoon. Pour the hot milk into the butter-flour mixture all at once. Add 1 tablespoon salt, the pepper, and nutmeg, and cook over medium-low heat, stirring first with the wooden spoon and then with a whisk, for 3 to 5 minutes, until thick. Set aside off the heat.

Step 4

Separate the mushroom stems from the caps and discard the stems. Slice the caps 1/4-inch thick. Heat 2 tablespoons of oil and 2 tablespoons of the butter in a large (12-inch) saute pan. When the butter melts, add half the mushrooms, sprinkle with salt, and cook over medium heat for about 5 minutes, until the mushrooms are tender and they release some of their juices. If they become too dry, add a little more oil. Toss occasionally to make sure the mushrooms cook evenly. Repeat with the remaining mushrooms and set all the mushrooms aside.

Step 5

To assemble the lasagna, spread some of the sauce in the bottom of an 8 by 12 by 2-inch baking dish. Arrange a layer of noodles on top, then more sauce, then 1/3 of the mushrooms, and 1/4 cup grated Parmesan. Repeat 2 more times, layering noodles, sauce, mushrooms, and Parmesan. Top with a final layer of noodles and sauce, and sprinkle with the remaining Parmesan.

Step 6

Bake the lasagna for 45 minutes, or until the top is browned the sauce is bubbly and hot. Allow to sit at room temperature for 15 minutes and serve hot.