Step 1

For nuoc cham, stir sugar and 100ml water in a small saucepan over medium heat until sugar dissolves (1-2 minutes). Cool (15-20 minutes), then stir in remaining ingredients and combine.

Step 2

Meanwhile, soak mung bean noodles in cold water until soft (30 minutes). Drain well, then cut into rough 5cm lengths with scissors. Set aside.

Step 3

Heat oil for deep-frying to 180C in a deep saucepan. Remove saucepan from heat, add taro gradually, allowing for oil to bubble up as you do, then when bubbles die down, return pan to heat and deep-fry, stirring occasionally, until taro is golden and crisp (3-4 minutes; be careful, hot oil will spit). Remove with a slotted spoon and drain on paper towels. Reserve oil.

Step 4

Heat 50ml oil in a large wok over medium heat, add onion and stir-fry until just tender (3-5 minutes). Add cabbage, carrot and celery and stir-fry until tender (3-5 minutes). Remove from heat, add kecap manis, oyster sauce and sugar, season to taste, then add fungi, noodles and taro, check seasoning and set aside to cool (45 minutes to 1 hour).

Step 5

Working with 4 spring roll wrappers at a time, place on a bench with a corner towards you. Brush edges with eggwhite. Add ¼ cup vegetable mixture to each down the centre in a line about 15cm long, fold corner closest to you tightly over the filling, then fold in sides and roll up to enclose, ensuring edges are sealed. Repeat with remaining rolls in batches. Spring rolls can be made ahead and kept frozen in airtight containers with baking paper between each layer for up to a month.

Step 6

Heat oil for deep-frying to 180C in a deep saucepan, add spring rolls in batches and deep-fry until golden and crisp (4-6 minutes). Drain on paper towels and serve with mustard leaves, Vietnamese mint and coriander for wrapping and nuoc cham.