Mix the milk and mayonnaise well with the whisk. Then add the sour cream and lemon juice and season with salt and pepper from the mill. Then mix in the appropriate amount of linseed oil (in the Spreewald it can even be a little more - but it takes getting used to).
Finely dice the pickles. Peel the onions and cut into thin rings. Leave the capers whole or cut in half and cut the herring fillets bite-sized. Stir everything into the sauce and let it steep for at least 24 hours.
Before serving, it can be garnished with chives rolls.