Pour herring from the package into a sieve and rinse off the oil under running water (as best you can). Then place the herring fillets in a bowl. Cut the onions into rings and the peeled apples into pieces and add to the herring. Add the peppercorns and pour the buttermilk over them. Chill the whole thing for about 24 hours.
Then enjoy with jacket potatoes.
Of course, the dish also tastes good with fresh herring.