Peel the potatoes, cut into pieces of equal size and cook.
When the potatoes are soft, drain off the cooking water and press the potatoes through a potato press into a bowl while they are still hot.
Press the potato mixture into the bowl and divide into four equal parts. Dig out one of these parts and set aside. Fill the “free” quarter with potato flour and put the dug up quarter back into the bowl.
You don't have to weigh the potato flour. The ratio of potatoes to potato flour is important. This is why it works well to fill ¼ of the potato mixture with potato flour.
Add the oil and salt and mix well with a spoon, then knead the dough until it is soft and smooth.
Shape the dough into equal sized dumplings.
Bring water to a boil in a large saucepan and season with salt. Put the dumplings in the boiling water and let them steep.
When the dumplings float to the surface, leave to steep for another 3-7 minutes, depending on the size of the dumplings.
Drain the dumplings and serve.