Cook the macaroni in a large pot of boiling salted water. Drain thoroughly.
Butter a gratin dish. Put in half the macaroni, half the cheese scattered over them and half the crème fraîche. Season with pepper and grate some nutmeg over them. Cover with the remaining macaroni, cheese and crèmefraîche.
Bake in the hot oven for about 30 minutes, till bubbling and brown on top. Couldn't be easier!