If you use brine fillets, rinse them in cold water before slicing. You may have to rinse a few times depending on how salty the herring is. If you have oil fillets, just dry them thoroughly with a paper towel since these herring fillets do not need to be soaked in water.
Wash the herring fillets and dry with paper towel. Cut into small bite size pieces.
In the meantime, peel the onion, slice it and pour about 1 tablespoon of sugar over it, mix, and let it stand for about 30 minutes to soften and absorb the bitterness.
Peel the apple and slice thinly lengthwise. I used Granny Smith apple.
Peel the pickled cucumbers and slice thinly lengthwise.
Mix sour cream and mayonnaise in a bowl.
Add the onion, apple and pickles. Then add salt, pepper, and crushed Juniper berries. Mix, taste and possibly add more spices to taste.
Finally, add cut up herring and stir all together. Transfer to a container, jar or bowl. Store in the fridge. Herring will taste better the next day, after all the ingredients bite through. Serve well chilled.