Melt the butter in a saucepan, add the flour and mix. Gradually add the cold milk while stirring. Add salt, pepper, and nutmeg. When the béchamel becomes slightly thick, add the mushrooms and remove from the heat.

Cook the chicken pieces in oil, then add them to the béchamel.

Place a layer of Warda lasagna sheets at the bottom of a buttered baking dish, pour a layer of chicken and mushroom béchamel sauce over it, add a layer of Gruyère cheese, and repeat the process three times. Bake in the oven for 40 minutes.