Adapted from the famous recipe by Barefoot Contessa by adding more veggies and less butter; still so rich and delicious though! Now, serves just for 4 but it's easy to serve more - just double the ingredients and put in a 9x13 pan.
Preheat your oven to 375°F Bring a large, wide pot of water to boil with salt and a splash of oil, that will help keep your noodles from sticking together as they drain. Add the lasagna noodles and cook for 10 minutes. Drain and set aside.
Make béchamel: Bring the milk and garlic to simmer in a saucepan, or heat it in your microwave, and set it aside. Melt 4 tablespoons butter in a large saucepan. Add the flour and cook for one minute over low heat, stirring constantly with a whisk or wooden spoon. Pour in the hot milk, a little at a time at first and stirring until combined. Continue adding a few tablespoons at a tim until you’ve added half of it, then you can add the second half all at once, along with 1/2 teaspoon table salt, the pepper, and nutmeg. Cook over medium-low heat, stirring or whisking frequently, for 3 to 5 minutes, or until thick. Set aside.
Prepare vegtables: Discard portobello mushroom stems and/or trim the ends of the cremini stems. Slice mushrooms 1/4-inch thick. Heat 1 tablespoon olive oil and 1 tablespoons butter over medium in the bottom of the large, wide pot you used to cook the noodles earlier, or in a large sauté pan. Cook the mushrooms with a pinch of salt for about 5 minutes, or until they are tender and release some of their juices, tossing to make sure they cook evenly. Add the spinach and cook until wilted.
Assemble lasagna: Spread some of the sauce in the bottom of 9x9 baking dish (if you’d like to freeze or give this dish as a gift, remember to use a foil pan). Arrange a layer of noodles on top*, then more sauce (about 1/4 of what remains), 1/3 of the mushrooms and 1/4 cup grated parmesan. Repeat two more times then top with a final layer of noodles, your remaning sauce and last 1/4 cup of parmesan.
Bake for 40 minutes, or until top is browned and the sauce is bubbly. Let sit at room temperature for 15 minutes before serving. To freeze for future use, allow it to cool completely and wrap two to three times in plastic wrap before freezing.