Boil potatoes until soft, peel and press through. Sieve the wheat flour into a bowl and mix with the yeast, potatoes and salt. Mix the whole thing with milk to form a smooth dough. Cover with a kitchen towel and let rise in a warm place for 20-30 minutes.
With oil-wet hands, pull fist-sized pieces of dough onto the size of a plate. Heat the oil in a saucepan and carefully place the Langosch on the hot oil surface. Turn after about a minute. Fry the second side until golden brown. Drain at the end. Serve with sour cream.