The origins of this pasticcio (baked dish) have been attributed to the chef of Tsar Nicholas II. Imperial or not, it is an excellent dish which is also extremely simple to make. It can be made quite successfully one or two days in advance and kept, covered, in the fridge.
Stir the parmesan and nutmeg into the béchamel sauce and keep it warm over a very low heat. Put a circle of greased greaseproof paper on top of the sauce to prevent a skin from forming.