Wash the firm potatoes thoroughly, place them in a large pot, cover with water, and bring to a boil. Cook for about 20 minutes until fork-tender.

Drain the water and let the potatoes cool completely, preferably refrigerating overnight.

Using a potato masher or ricer, crush the cooled potatoes until smooth and lump-free.

Combine smooth mashed potatoes with egg, potato starch, salt, and a pinch of nutmeg in a mixing bowl.

Mix everything until a soft, cohesive dough forms, ensuring no dry spots of potato starch remain.

Dust hands with potato starch, divide the dough into portions, rolling each into a ball about the size of a golf ball.

In a large pot of salted water, bring to a gentle boil and drop the dumplings in carefully, avoiding overcrowding.

Cook for 10-15 minutes until dumplings float to the surface, then remove with a slotted spoon and drain.