While spring rolls are delicious at any time of year, many Chinese cooks prepare them during the Lunar New Year because of their resemblance to gold bars. Making homemade wrappers is very difficult because the dough is so soft. I buy the spring roll wrappers, which you can usually find in the frozen-food section of supermarkets. Chinese wrappers are different from Thai and Vietnamese spring-roll wrappers, which are made of rice flour (instead of wheat) and need to be soaked in water to be pliable. Buy square wrappers that are about 16cm (6in) across.
Fresh bamboo shoots can be purchased with the tough outer leaves intact, or peeled. I buy the whole ones, but if you want to make life a little easier, buy the peeled one (you can sometimes find them in the frozen food section of supermarkets). A 350g (12½oz) unpeeled bamboo shoot yields about 250g of flesh.
Briefly rinse the mushrooms under running water, then put them in a bowl and add warm water to cover them. Soak the mushrooms for about two hours, or until fully hydrated.
While the mushrooms are soaking, prepare the other ingredients. Rinse the bean sprouts then leave them in a colander to air-dry.
Cut the pork belly into fine strips about 2cm (⅞in) long, then put them in a bowl and add the soy sauce, rice wine, sugar, a quarter of a teaspoon of salt, the white pepper, cornstarch and 10ml (2tsp) of cooking oil. Mix thoroughly then leave at room temperature to marinate.
Peel the bamboo shoot, removing the tough leaves until you reach the tender flesh. Cut the bamboo into thin matchsticks, with pieces that are about 2½cm (1in) long. Bring a pot of lightly salted water to the boil, add the bamboo pieces and simmer for three minutes before draining.
Peel the shrimp, leaving the tail intact. Devein the shrimp: cut a small slit on the back close to the tail, then carefully pull out the dark digestive tract. Without cutting all the way through to the back, slice the shrimp along the entire length of its front side, then open it so it lays flat.
When the mushrooms are fully hydrated, squeeze them to remove the excess liquid, then cut off and discard the stems. Cut the caps into fine dice
Heat a wok over a high flame until very hot, then add about 10ml (2tsp) of oil. Add the bean sprouts, sprinkle lightly with salt then stir-fry briefly, just until the sprouts start to wilt. Transfer them to a bowl. Heat about 10ml (2tsp) of oil in the wok, add the mushrooms, bamboo and about ¼tsp of salt and stir-fry for about a minute before putting the ingredients into the bowl with the bean sprouts. Heat 15ml (1tbsp) of oil in the wok, add the pork and stir-fry until the meat loses its pink colour. Add the vegetables back into the wok and stir-fry until thoroughly combined. Taste the mixture and correct the seasonings, if necessary. Put the ingredients into the bowl and cool to room temperature, stirring often to release the steam.
Stack the spring-roll wrappers on a plate and cover with a clean dishcloth. Put one wrapper on a cutting board, with one corner pointing towards you. Lay a 7cm-long (2¾in) strip of filling on the wrapper, close to the near corner. Fold up the bottom of the wrapper over the filling then fold in the sides. Roll away from you until you reach about a third of the way, then lay one shrimp down so just the tail is sticking out. Continue to roll until you almost reach the other side. Very lightly brush egg on the far edge, then finish rolling. Put the spring roll seam-side down on a baking tray lined with cling-film. Repeat with the remaining wrappers.
Heat oil to a depth of about 2cm (⅞in) in a skillet. When the oil is 180°C (350°F), fry the spring rolls in batches until pale golden, then drain on paper towels. After frying all of the spring rolls, briefly fry them for a second time in the hot oil, cooking them for only about 30 seconds (double frying makes them crisper). Drain on paper towels.
Mix some brown vinegar with minced ginger. Stack the spring rolls on a platter, then then serve with the dipping sauce.