Boil the potatoes in salted water and peel them. Soak bread in milk. Wash the mushrooms and cut them in small pieces. In less fat fry them together with the finely chopped onion (until water evaporates and remain fat). Pull the fire and add to mushrooms, grated potatoes, well drained of milk bread, 4 egg yolks, parsley and universal spice. Stir well. The mixture shaping meatballs (the size of a tangerine), roll in bread crumbs, then dip in slightly beaten whites and again in breadcrumbs. Pressuring well each meatball to get tight ball. Leave to rest for 10 minutes away (to tight). Fry meatballs until golden.