First wash the potatoes under running water, put them in a saucepan, cover with plenty of cold water and bring to a boil.
After 20-30 minutes from boiling, the potatoes should be cooked (try the skewering a potato with a fork: if it slips easily, the potato is cooked).
Drain the potatoes and place them in a bowl filled with cold water, then peel them.
Mash with a potato masher, then add egg, parmesan, at least 1 teaspoon of salt and pepper and mix well.
Fry in already warm seed oil, turning them to make them evenly browned, then drain them on absorbent paper.
Let it cool slightly, then cut them in half and fill them.
Your croquette is ready, serve immediately.