Season chicken thighs with salt and pepper.

Sear chicken in a pan with 2/3 of the olive oil and 1/2 of butter until browned on all sides.

Add smashed garlic, fresh sage leaves, and lemon zest to the pan. Stir.

Pour in milk (enough to almost cover the chicken)

Add the dried wild mushrooms.

Simmer gently until the chicken is cooked.

Remove chicken and shred when cooled.

Strain and reserve the milk, discarding the garlic, sage, and lemon zest.

Sauté leeks and mushrooms in 1/2 of the butter in a separate pan and 1/3 of the olive oil until softened.

Season with salt, pepper, and fresh thyme.

Cover and cook until liquids evaporate.

Set aside.

Melt the butter in a saucepan, then add the all-purpose flour to create a roux.

Add gradually reserved milk (top it up to 2 liters) while stirring to avoid lumps. Cook until thickened.

Add leftover mushrooms (from the chicken mixture) and season with salt and pepper.

Cook until the sauce is well-flavored and smooth.

Preheat the oven to 180°C (350°F).

Butter a baking dish and rub it with garlic and salt.

Divide the filling ingredients into 3 parts while dividing the bechamel into 4 parts since we need an extra layer for the top.

Lay lasagna sheets, allowing them to extend over the sides.

Layer with a portion of leeks, mushrooms, chicken, and a drizzle of bechamel sauce.

Repeat the layering process until the ingredients are used up, finishing with lasagna sheets on top.

Pour the remaining bechamel sauce over the top layer of lasagna.

Sprinkle with the grated pecorino cheese.

Cover with double foil and bake for approximately 45 minutes at 180°C (350°F).

Remove the foil and bake for a few minutes until the top is golden brown.

Allow the lasagna to rest before slicing and serving.

Enjoy your Chicken Mushroom Lasagna with Creamy Leeks!