For the potato balls, peel and rinse the potatoes. Cook in salted water for 20 minutes. Drain the water. Steam the potatoes and let them cool.
Then press through a potato ricer into a large enough bowl. Mix with egg yolks, Parmesan cheese, butter, salt and nutmeg to make a smooth dough.
Use a teaspoon to cut the dough and form small balls. Turn the potato balls first in beaten egg, then in breadcrumbs on the other side.
Heat oil in a deep fryer to 180 °C. Fry 4 to 5 potato balls at a time in the fat for 2 minutes until light brown. Keep warm until all the balls are done.