Prepare the béchamel: In a saucepan, melt the butter over medium heat. Whisk in the flour until smooth, then gradually add milk, stirring until thickened and creamy, around 5-7 minutes.

Season the sauce: Add a pinch of freshly grated nutmeg and salt to taste, letting the flavors meld together while you prepare the other ingredients.

Sauté the mushrooms: In a skillet, heat some oil and add chopped onions and minced garlic. Sauté until fragrant, then add sliced mushrooms, cooking until they are soft and golden, approximately 8-10 minutes.

Assemble the layers: In a baking dish, spread a layer of béchamel sauce at the bottom. Layer with lasagna noodles, sautéed mushrooms, and more béchamel. Repeat until all ingredients are used, finishing with a béchamel layer on top.

Add the cheese: Generously sprinkle shredded cheese over the top layer. If desired, cover with a sprinkle of fresh herbs for an aromatic touch.

Bake the lasagne: Preheat your oven to 375°F (190°C) and bake for 25-30 minutes, until bubbly and golden brown on top. Let it cool for a few minutes before slicing.