Boil potatoes in their skins for 20-30 minutes, then peel and mash until smooth.

Beat in half the salt, the eggs and nutmeg, then gradually add the flour until you have a smooth, elastic dough which comes away from the sides of the bowl.

Divide into small pieces and roll on a lightly floured surface until you have a rope as thick as a finger, then cut into 1"/2 cm pieces.

Drop gnocchi into salted, boiling water.

When they rise to the surface, they're done—about 5 minutes.

Remove and drain.

Heat oven to 400°F./200°C.

Place gnocchi in baking dish and put butter on top.

Slice enough cheese to cover, then season with the rest of the salt and some pepper.

Cook in the oven for 15 minutes or until cheese browns on top, then place on individual serving dishes and cover with heated tomato sauce.

Sprinkle with grated cheese and serve immediately.