Peel the potatoes and cut them into smaller pieces.
Put the potatoes in a pot with lightly salted water.
Boil them until they are completely tender.
Drain the water and mash the potatoes, it can just be done with a fork.
Mix potato flour, butter, grated parmesan, egg, and milk into the potatoes and stir together - possibly with your hands. It should become a rather sticky dough.
With wet hands, form 12-16 balls from the potato dough.
Flatten each ball into a pancake shape, and place 2 tbsp of filling in the middle of each pancake.
Fold the potato dough around the filling and shape it into a ball. Keep your hands moist so the dough doesn't stick.
Place each finished dough ball on a plate/cutting board sprinkled with flour.
You can advantageously freeze them for 1-2 hours, so they are easier to bread and cook.