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