Step 1 Bring a large saucepan of water to the boil. Remove 12 large outer leaves from wombok. Cut out the V shape from the thicker stalk and discard. Add wombok leaves, in batches, to pan; cook for 2 minutes, or until leaves are soft. Remove with tongs and drain. Rinse leaves under cold running water; drain again and set aside.
Step 2 Place ginger, garlic, spring onion, sesame oil, fish sauce and coriander in a small food processor; blend until mixture is finely chopped. Add lime juice and water chestnuts; process mixture until chestnuts are finely chopped. Transfer mixture to a large bowl, add pork and stir until combined.
Step 3 Place 1 wombok leaf on a flat work surface. Place 1 heaped spoonful of the pork mixture about 3cm from the end of the wombok leaf. Roll up leaf to enclose mixture, folding in the sides as you go. Repeat with remaining wombok leaves and pork mixture. (To prevent rolls from unrolling, arrange them so they’re touching.)
Step 4 Line a bamboo or metal steamer with a sheet of baking paper; place rolls on paper. Cover and steam for 6–7 minutes, or until pork is cooked through.
Step 5 Plate up 3 rolls per person and serve with sweet-chilli sauce and a side of steamed vegies.