Boil the potatoes, sieve and kneed together with the flour and egg; boil the gnocchi in salted water; remove them with a perforated ladle as soon as they float to the surface. Place them in a buttered oven pan, alternate with thin slices of fontina PDO, curls of butter, pepper and nutmeg. Finish with a layer of fontina and bake in the oven for 15 minutes, until the fontina PDO melts to form a homogeneous cream.