Begin by boiling the potato with the skin on. You need more than 500 g because you'll be weighing it when it’s cooked and peeled. Cook the potato about 5 minutes longer than usual.
Set the cooked potatoes aside to cool, then peel and mash them. The easiest and most proper way is to run potatoes through a ricer. But if you don't have one (like I don't), you can grate it!
You may end up with small lumps of potato in the dough but this is no big deal. This is why I slightly overcook it so it's easier to break up the lumps as I knead.
Add flour, lard, egg and a pinch of salt. Of course, you can substitute lard with butter but my grandmother always stuck to lard.
Gently combine all the ingredients with your hand. At one point, the dough will come together and won't stick to the bowl.
Don't over-knead the dough because the more you work it, the more moisture the potatoes release. Then you need extra flour, which only makes the dumplings hard and chewy.