First boil the potatoes, let cool and peel. Slice the potatoes and the apple, sprinkle the latter with lemon juice so that it does not turn brown.
Steam the vegetable mixture and let it cool, dividing any pieces that are too large.
Strain the herrings and cut them into larger pieces, removing the bones if necessary.
Season the mayonnaise with the sour cream, a little mustard, salt, herb salt and pepper. Finely chop the marinated onions if necessary, add them, mix well and mix with all the chopped ingredients. Leave in a cool place for a few hours.
Peel the boiled eggs, cut them into quarters and garnish the salad with them.