Recipe:
Brine sardines in a 10% salt solution for 48 hours. Shorter than this and the fish turn out mushy, longer and they’re too salty.
Rinse brine off, put fish in a jar with ~65% vinegar solution and whatever spices you like. I use bay, onion, pepper and junpier.
Wait 4 days before eating. Obviously it needs to be kept in the fridge.
Quite a treat when you do. Here you might see them frozen in shops but be careful - they’re so so high in polyunsaturated fatty acids that they go rancid quickly even when frozen!