1. Prepare the Noodles
Bring a large pot of salted water to a boil. Cook the lasagna noodles until al dente. Drain and lay them flat on a clean towel to prevent sticking.

2. Sauté the Vegetables
Heat olive oil in a skillet over medium heat. Add sliced mushrooms and cook until browned and tender. Add spinach and sauté until wilted. Stir in nutmeg and season with a pinch of salt.

3. Make the Béchamel Sauce
Prepare a béchamel sauce from scratch by whisking butter, flour, and milk until smooth and creamy. Season with salt and pepper to taste. Alternatively, use a high-quality store-bought version.

4. Assemble the Lasagna
In a 9×13 baking dish, start with a thin layer of béchamel sauce. Add a layer of noodles, followed by mushroom-spinach mixture, mozzarella, and parmesan. Repeat layers, finishing with sauce and cheese on top.

5. Bake
Preheat oven to 375°F (190°C). Cover lasagna with foil and bake for 25 minutes. Remove foil and bake an additional 10–15 minutes until bubbly and golden. Let rest 10 minutes before slicing and serving.