Pork(List of the Ceremonial Animal)::Kidney
Stir-fry kidney slices until well-done and they will be tough and as dry as wood. But serve them tender and they will leave people doubting their doneness. It is more preferable to braise the kidneys until soft  and eat it dipped in Szechuan pepper salt. Alternately, it can also be finished with the preferred seasonings.
To clean the kidneys, pluck out their insides by hand, but do not cut them with a knife.  One needs to braise kidneys for a whole day before they are tender and soft as mud. Kidneys should only be cooked on their own , and never used with other ingredients since their off-flavours would overpower everything else. Braise for only three ke  and kidneys will toughen but braise them for a day and they become tender.
: It seems tastes in Chinese foods have changed since Yuan Mei’s time. These days, kidneys are rarely eaten braise to the point of extreme softness (soft as mud) as he suggested! Rather, most modern Chinese preparations involve rapid cooking to maintain the crisp texture of the kidneys. A perfect example of this is “stir-fried kidney flowers” (爆腰花), where the clean and prepared kidneys are cut in the lychee pattern (荔枝型) or wheat sheaf pattern (麦穗型), parboiled to deodorize them, and rapidly stir-fried in burning hot oil.
: The white coloured insides of the kidney, known as the renal pelvis, is where urine filtered from the blood is collected and sent to he bladder. They are likely tough when cooked and potentially stink as well which justifies their removal thourough. I doubt it’s easy to do this without using a knife though.
: It is for this reason precisely that I don’t like steak and kidney pie. Or maybe that “special” flavour is just an acquired taste.
: One ke (刻) amounts to around a quarter of an hour.