Peel, rinse and boil the potatoes in salted water. Then mash them while they are still hot. Slightly cool them.
Put the raw egg, 2 tbsp of breadcrumbs, dairy butter, sour cream, salt, pepper in the still warm mashed potatoes; stir it up well.
Peel and dice the onion, and then brown it in vegetable oil.
Rinse and chop the mushrooms, add them to the onion, fry them with onion until ready (some 10-20 mins). Cool it.
Shape the 5mm thick circles of mashed potatoes, and then put the mushroom stuffing in the middle of it. Roll them up.
Dip the potato rolls in breadcrumbs, and then fry from all sides in the vegetable oil. Put them onto paper napkin to get rid of oil’s excesses. Serve hot with sour cream or mushroom sauce.