Like so many other preserved Chinese ingredients, Tianjin preserved vegetable (dong choi) is pungent. You can smell it even through the sealed earthenware jars it is sold in. Depending on your perspective, the smell is garlicky and mouthwatering, or repulsive. To make dong choi, celery cabbage is salted, which draws out any excess moisture and preserves it. It is then chopped, flavoured with garlic and spices and then packed into small jars. Dong choi keeps indefinitely, but if you want to prevent its smell from permeating everything in your fridge or pantry, it's best to seal it in a glass container. The salty, garlicky flavour of dong choi is used in soups, noodle dishes, stir-fries and steamed dishes. It's used straight from the jar - there's no need to rinse it. Because it's so strong, the vegetable should be used in small quantities. If you've eaten the popular dish known as 'dry-fried string beans', you've probably had dong choi (some places use other types of preserved vegetables). Soak dried shrimp in warm water for about 30 minutes then drain (reserve the liquid) and chop roughly. Heat about 200ml of oil in a wok until it reaches about 180 degrees Celsius. Rinse the string beans, pat dry and cut into 6cm lengths. Add the string beans to the wok and cook, stirring constantly, until they become wrinkled and blistered. Remove the string beans from the wok and pour off most of the oil. Stir-fry a chopped clove of garlic until fragrant then add the dried shrimp and about one heaped tablespoon of dong choi and stir-fry for about 30 seconds. Add a little minced pork, some sugar, white pepper, rice wine and a small amount of soy sauce and stir-fry until the meat starts to lose its pink colour. Add the string beans and some of the soaking liquid from the dried shrimp and cook over a high heat until the liquid is absorbed. Taste for seasoning then stir in the minced spring onions and serve immediately. To make a quick Chinese soup, marinate slightly fatty minced pork with soy sauce, rice wine, sugar, salt, white pepper and a little cornstarch. Soak dried shrimp and Chinese mushrooms in warm water (they can be soaked together). When the mushrooms are soft, cut off the stems and dice the caps. Drain the shrimp and reserve the soaking liquid. Heat about 30ml of oil in a pan, add a few slices of fresh ginger and cook until fragrant. Stir in the minced pork and cook until it is no longer pink, then add the dried shrimp, diced mushrooms and some dong choi. Stir in the shrimp/mushroom soaking liquid and some plain water then cover and simmer for about 15 minutes. Add a vegetable of choice (sliced Chinese radish or baby pak choi are good) and simmer until cooked then taste the broth for seasoning. Sprinkle with minced spring onions, drizzle with sesame oil and serve.