Cut herring, cucumber and onion. Mix with the remaining ingredients and let steep in a closed bowl in the refrigerator.
It may be that the thick sauce caused by the sour cream has to be diluted a little with a dash of milk. The mass should have the consistency of yogurt. Just sleep one more night and then enjoy with fresh jacket potatoes.
All additional things like apple etc. are a matter of taste and should only be tried the second time. The original is pure and without a lot of frills.