1.Peel the potatoes and cut in half if they are large. Try to make them all a similar size so they will cook at the same time. Place in a large saucepan of cold salted water and bring to the boil. Boil for 10-15 minutes, depending on the size of the potatoes, or until a skewer easily goes into them.
2.Drain the potatoes and return to the hot saucepan to make sure they are dry. Put the potatoes through a potato ricer or a mesh sieve. It is important that they are mashed very finely. Scatter the flour over the potatoes, add the egg, and stir with a wooden spoon until it comes together in a dough. Season to taste with salt and pepper.
3.Gently knead the dough on a lightly floured surface for only as long as is necessary to bring it together in a smooth ball. Roll the dough into a large sausage and cut it into eight pieces. Roll one piece into a sausage about the thickness of your thumb and cut into 2cm lengths. Roll one piece into a ball and gently roll the ball down the tines of a fork. Place the gnocchi onto a heavily floured tray. Repeat with the remaining pieces of dough.
4.Bring a large saucepan of well-salted water to the boil. Simmer the gnocchi, in batches, for about 2 minutes or until they rise to the surface. Once they are floating, they are cooked. Remove with a slotted spoon.
5.Heat the butter and sage in a large frying pan over medium heat until the butter is melted and starting to turn golden brown. Tip the gnocchi into the pan and toss through the butter to coat the gnocchi well. Season to taste with salt and pepper.
6.Serve the gnocchi and butter in warmed bowls; top with parmesan. Serve with salad, if desired.
Uncooked gnocchi suitable to freeze. Not suitable to microwave.Note