Cook chopped pork in a wok over medium heat. After 3 minutes of cooking add chopped prawns (if desired). Cook until pork is no longer pink. Drain, season with salt and set aside to cool.
Mix together spring onions, ginger, soy sauce, rice wine, oil, sugar and pepper. Stir in meat mixture. Stir in water and mix thoroughly. Chill in freezer for 2 hours, or in refrigerator overnight to firm up and blend flavours.
Prepare the recipe for Hom bao (Chinese steamed buns).
Shape dough into balls. Roll each out into a circle. Put 1 tablespoonful of prepared meat mixture in the centre of each circle, and wrap dough around filling. Place seams down onto squares of greaseproof paper. Let stand until doubled, about 30 minutes.
Bring water to a boil in wok, and reduce heat to medium; the water should still be boiling. Place steam-plate on a small wire rack in the middle of the wok. Transfer as many buns on the greaseproof paper as will comfortably fit onto steam-plate leaving 2.5 to 5cm (1 to 2 in) between the buns. At least 5cm (2 in) space should be left between steam-plate and the wok. Cover wok with lid. Steam buns over boiling water for 15 to 20 minutes.
REMOVE LID BEFORE you turn off heat, or else water will drip back onto bun surface and produce yellowish "blisters" on bun surfaces. Continue steaming batches of buns until all are cooked.