The secrets to a delicious kidney dish lie in cleaning the organs thoroughly and not overcooking them. They shouldn’t have any whiff of “barnyard”; if they do, I’ve heard that soaking them in milk will rid them of the pong, but it’s better to use well-cleaned kidneys in the first place.
Lamb kidneys have a much milder flavour than most other types. When you buy them, the vendor will often ask if you want them cleaned: if yours does, accept, with pleasure. If you can't find them at your regular market, go to a butcher that specialises in kosher or halal products.
Once all the ingredients have been prepared, this dish takes less than five minutes to cook. If you overcook the kidneys, they will be tough. Because kidneys (and other organ meats) are filling, this amount will serve more than the equivalent of another type of meat.
If using whole kidneys, remove and discard any fat and membrane from the exterior. Slice the kidneys in half lengthwise to reveal the interior, then remove the white core and any veins (I snip them out with kitchen shears).
Sprinkle the kidneys liberally with salt, place them in a colander and leave for about five minutes. Thoroughly rinse the kidneys with running water then dry them with paper towels.
Lay the kidneys cut-side down on a cutting board and score the exterior in a cross-hatch pattern. Cut the kidneys into bite-sized pieces and set them aside.
Put the Sichuan peppercorns in a small, unoiled skillet and place over a medium flame. Stir constantly for about about 30 seconds, or until the peppercorns are fragrant and lightly toasted. Crush them lightly in a mortar, then remove and discard the seeds (they're dark and shiny).
Thinly slice the garlic cloves. Trim the leaves from the Chinese celery stalks and set them aside to use as a garnish. Cut the stalks into 2.5cm (1 inch) lengths. Cut the bird's-eye chillies into thin rings, squeezing out and discarding the seeds as you go. Cut the banana chilli in half lengthwise and scrape out and discard the seeds. Thinly slice the chilli.
Heat a wok over a high flame and, when it’s hot, add the oil. Add the cumin seeds and let them sizzle briefly, then mix in the dried red chillies. Stir them until they darken slightly, then add the celery, garlic and bird's-eye and banana chillies and cook, stirring often, for about 30 seconds.
Add the kidneys to the wok and stir-fry until they start to lose their pink colour. Mix in the Sichuan peppercorns and soy sauce.
Stir-fry over a high flame until the kidneys are cooked – they should still be a little pink inside. Taste for seasonings and mix in a little salt, if necessary.
Transfer to a plate then garnish with the reserved celery leaves before serving with steamed rice and stir-fried green vegetables.