Liver is available from most animals we eat but those most commonly seen in cookbooks are calves', lamb's and chicken livers.
Today's breeding methods mean that calf's and lamb's liver tends to be milder in flavour than in times past, so it is not generally necessary to soak liver in milk before cooking unless you happen to have the stronger-tasting pig's or ox liver.
Liver is best cooked briefly over a high heat. Large livers should be sliced thinly (and beaten with a mallet if desired) but chicken livers are usually small enough to fry whole.
Livers can be fried with onions and bacon, made into pâtés and terrines. Chicken livers are good sautéed with olive oil and lemon and served as mezze or in salad; they also make a rich addition to risotto.