Preheat your oven to 375°F (190°C).

Cook the lasagna noodles according to package instructions until al dente, about 8-10 minutes. Drain and lay flat to prevent sticking.

In a large skillet, heat a drizzle of olive oil. Add minced garlic and sliced mushrooms, sautéing for about 5-7 minutes until tender. Stir in fresh spinach and cook until wilted, about 2-3 minutes. Set aside to cool.

In a medium saucepan, melt 4 tablespoons of butter over medium heat. Add 4 tablespoons of flour to make a roux, stirring for about a minute. Gradually whisk in 3 cups of milk, cooking until thickened, about 5-7 minutes. Season with salt, pepper, and a pinch of nutmeg.

In a baking dish, spoon a thin layer of béchamel sauce, layer noodles, half the spinach and mushroom mix, and mozzarella. Repeat until all ingredients are used, finishing with béchamel and a final layer of cheese.

Cover the dish with aluminum foil and bake for 25-30 minutes. Remove the foil and bake for an additional 15 minutes until golden.

Let the lasagna sit for 10-15 minutes before slicing and serving warm, optionally with a side salad or garlic bread.