1. Place the potatoes in a pot, cover with water and bring to a boil. Simmer until fork tender. Drain potatoes when tender and remove skins when they are cool enough to handle.
2. Press the cooked potatoes through a ricer or coarsely grate them into a large bowl. Mix the yolk into the potatoes with a wooden spoon until well blended.
3. Transfer the mixture to a lightly floured surface. Knead in a small amount of flour at a time until the dough is smooth but still slightly sticky. Season with salt and freshly ground white pepper.
4. Form the dough into 1 large log and cut into 4 sections. Roll each section into a long cigar shape about 1/2 inch in diameter.
5. Cut into 1/2-inch pieces and delicately indent by pinching the pieces in the middle. Dust well with flour.

Cooking

1. To cook, bring a pot of salted water to a boil, add gnocchi and cook for 2-3 minutes or until the gnocchi begin to float to the surface.
2. As they surface, remove with a slotted spoon and drain well.
3. They can be tossed in a heated sauce before serving.