Cook potatoes with the peel in a large pot with boiling water until fork-tender, then drain the water.
Let cool, then peel the potatoes (the weight of the cooked and peeled potatoes was 750 g). Mash them with a potato masher.
Add potato starch, salt, and nutmeg. Use your hands to knead the mixture into a smooth dough. Meanwhile, bring water and enough salt in a large pot to a simmer.
Wet your hands, take a handful of dough, and shape it into a ball. The recipe makes 6-8 potato dumplings, depending on how large you make them. You can fill some of them or leave them all plain (check the notes below for my mushroom stuffing recipe).
Reduce the heat of the pot. The water should be hot (about 80-85 degrees C resp. 176-185 degrees F) but it shouldn't boil or simmer. Carefully add the potato balls into the pot and let them cook in the water for 15 minutes, they will rise to the surface.
Remove them from the water with a slotted spoon. Serve and enjoy!