Although this is a Chinese dish, I like to use sakura shrimp - tiny, pink dried shrimps that are sold in packs in the Japanese food sections of supermarkets. They have a more delicate texture and flavour than Chinese dried shrimp, and don't need to be soaked in water. If you can't find sakura shrimp, use Chinese dried shrimp, but this adds about 15 minutes to the preparation time, to give them time to soak in hot water.
Long beans are also called snake beans or yard long beans. Dried shrimp roe (ha ji) is usually sold in small glass jars. The roe is tiny and looks like reddish-brown dust, but it has a strong flavour. You can leave it out, if you wish. Cha choi (Sichuan preserved mustard stem, also called zha cai) comes whole (as a large lump covered with a red-orange paste), or cut into strips and sold in packages. If buying the whole piece, rinse it thoroughly to remove most of the red chilli-paste coating before slicing it.
Put the pork in a bowl then add the soy sauce, rice wine, sugar, salt, pepper and cornstarch and mix thoroughly. Briefly rinse the sakura shrimp then drain them before blotting with paper towels. If using Chinese dried shrimp, put them in a bowl, add about 60ml (¼ cup) hot water and soak for about 15 minutes, or until pliable. Drain the shrimp, reserving the soaking liquid. If the shrimp are large, cut them into smaller pieces.
Cut the long beans into 5mm (¼in) pieces. If using whole cha choi/Sichuan preserved mustard stem (you won’t need the whole piece), rinse it and dry it. Whatever type you’re using, cut it into small dice. Cut the garlic clove in half. Halve the bird’s-eye chilli lengthwise and scrape out and discard the seeds. Finely mince the chilli.
Heat a wok over a high flame and, when it’s very hot, add about 10ml (2tsp) of cooking oil. When the oil is hot, add the shrimp and stir-fry constantly for about 30 seconds, or until fragrant. Use a metal spatula to take the shrimp from the wok, leaving behind as much oil as possible. Add the garlic and chilli and stir for about 10 seconds. Add the marinated pork to the wok and use the spatula to break it up into smaller pieces. Stir-fry over a high flame until the pork starts to lose its pink colour, then remove the meat, garlic and chilli from the wok.
Pour about 10ml (2tsp) of oil into the wok and place it back over the flame. When the oil is hot, add the long beans. Stir constantly over a high flame for about 30 seconds, then add the pork and shrimp back to the wok. Mix the ingredients together then add the cha choi and about 30ml (2tbsp) of water (or the shrimp soaking liquid) and stir well. Scrape all the ingredients to the centre of the wok then lower the flame and cover the wok with the lid.
Cook, stirring occasionally, until the long beans are crisp-tender. If the mixture seems dry, add more water (or shrimp soaking liquid). Mix in about a quarter of a teaspoon of shrimp roe (if using). Taste for seasonings and correct, if needed.
Transfer the ingredients to a serving dish and sprinkle with a little more shrimp roe. Serve immediately with steamed white rice.