Mix the sour cream, dill, fennel, lemon juice and peel in a bowl that is large enough to contain all the ingredients. Fold in the herring.
Cover and leave to stand in the fridge for a couple of hours to allow the tastes to meld.
500 g. (18 oz.) fillet salt herring, cut up into bits 3 dl. (10 fl. oz.) sour cream 5 tbs. finely chopped dill 1 small, finely chopped fennel bulb Peel and juice of half a lemon