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.
It’s pretty good book. It does lack on recipes(it has some) but it has a lot of information on tools, process, science and history. Even if you don’t make anything it’s still a good read.
Edit: Here’s the contents.