Bottarga is a form of preserving fish eggs with salt. Its a delicacy all over the Mediterranean and has a very ancient history. The great thing about it is, that it turns the fish eggs into a chewy salty speciality and means they can be kept for long periods of time. Our italian friend and colleague Giulio di Sabato used herring eggs with a technique he'd seen in Sardinia. The herring eggs are something we see a lot of here, and essentially a by-product, but one which can be used to make these optimum little treats. If you see the eggs in there when you open up a fresh fish, take them out, keeping the membrane attached. Leave the eggs in a saturated water salt solution 37% salt, over night. the next day remove them and roll them in salt, as much as will stick to it. keep 'em in the fridge and the next day wash, dry and repeat (and so on). when you have something which yields slightly under pressure and feels in some sense elastic your ready to slice or grate it until your heart's content.