Drain the oil from the salted herring. Put the cream in a salad bowl, add salt, pepper and sugar, stir until smooth. Chop the onion, apple and pickled cucumbers into cubes of 1 centimeter and add to the drain. Cut the herring into small pieces, add to the butter cream and put into the refrigerator for 12-24 hours. Boil the potatoes in their jackets and served with herring cream, sprinkled with dill.