Steam the potatoes for 30-45 minutes, when a skewer penetrates but they are still firm.
Peel them and mash them while they’re still hot . Season the potatoes with a pinch of salt and flour to obtain a fairly firm, smooth, non-sticky dough. Exactly how much flour will depend upon how moist the potatoes are.
Roll the dough out into snakes about as thick as your finger, cut the snakes into one-inch pieces, and gently score the pieces crosswise with a fork.
Cook the gnocchi in salted boiling water, removing them with a slotted spoon after they rise to the surface. Drain them well and serve them with a few leaves of sage, melted butter and Parmigiano cheese or a tomato sauce.