Place the unpeeled potatoes in a pot of water, bring to the boil and cook until tender. Drain and allow to cool slightly. Peel and mash. Place mashed potatoes onto a work surface and add flour. Mix together to form a ball. Hollow out a small well in the centre, add the egg, and mix well. Knead dough until smooth and firm, adding more flour if necessary. Cut dough into 4 pieces, rolling each out into a long thin sausage shape, around 2cm in diameter. Then cut roll into pieces of 2 to 3cm, shape each dumpling into an oval and lay the prongs of a fork flat against the dough to form an indent. This ensures that the sauce will stick. Place gnocchi on a floured surface and sprinkle more flour. Bring a large pot of salted water to the boil. Drop in a few gnocchi at a time; when they rise to the surface, remove with a slotted spoon. Serve immediately with desired sauce.