In a large mixing bowl, combine the finely chopped herring, optional meat, potatoes, beets, apple, onion and pickle. Mix 3 tablespoons of the dill with the vinegar, add salt and pepper to taste. Pour over the salad and toss gently with a wooden spoon. DRESSING: Remove the yolks from the hard cooked eggs. Mince the whites and set them aside. Force the yolks through a sieve into a small bowl with the back of a large spoon, then mash them to a paste with the tablespoon of prepared mustard. Gradually beat in the vinegar and oil, then the cream, a tablespoon at a time, until the sauce has the consitency of heavy cream Pour over the salad, mix lightly but thoroughly, cover and chill for at least 2 hours. Just before serving, transfer the salad to a large serving bowl or platter and sprinkle it with the minced egg whites and remaining chopped dill. SAUCE: Stir the beet and lemon juice into the sour cream until it is smooth and well blended. Pass this sauce separately.