Soak dried mushrooms in 300ml water for 1 hour.
Rinse sauerkraut, then simmer in boiling water for 30 minutes and drain.
Finely chop mushrooms and reserve the soaking liquid.
Sauté sauerkraut and mushrooms in butter with reserved water until liquid evaporates.
Boil potatoes in salted water for 20 minutes until soft and drain.
Fry diced onions in oil for 5 minutes until brown and reserve 1 tablespoon for garnish.
Mix flour, salt, oil, and water into a soft dough.
Knead dough for 8 minutes and rest for 20 minutes.
Mash cooled potatoes with cottage cheese and fried onions.
Roll dough to 3mm thickness and cut into 10cm rounds.
Fill dough rounds with fillings and seal edges with water.
Poach dumplings in boiling water for 4 minutes until they float.
Serve with soured cream, garnished with reserved onions and dill.