Wash potatoes, cook, peel and cut into 1 cm sized cubes. Chop herrings and pickles likewise into approx. 1 cm large cubes. Peel apples and remove core and seeds, dice. Peel onion, chop finely. Mix potatoes, pickles, herrings, apple cubes, onion and beans.
Prepare mayonnaise: Mix egg yolk, mustard, lemon juice, salt and pepper until smooth. Add oil drop by drop while constantly mixing until the mayonnaise becomes thick. Then add a bit more oil. Mix until the oil is used up, taste. Mix sour cream into mayonnaise, add vinegar, salt, pepper, horseradish, anchovy paste and capers to make a savoury marinade.
Let the salad rest, season to taste again with vinegar or lemon juice, salt and pepper. Decorate with hard boiled egg-quarters, possibly a bit of parsley, a few finely chopped capers and pickles cut into a fan shape before serving.