Peel the prawns and gently pull out the dark vein from each prawn back, starting at the head end. Place in a cloth and squeeze out the moisture. Put the prawns in a food processor and process to a coarse paste.
Put the prawn meat, water chestnuts, pork, 2teaspoons of the soy sauce, 2teaspoons of the rice wine, ½teaspoon of the sesame oil, the ginger and cornflour in a bowl. Season well and stir vigorously to combine.
Put ateaspoon of filling in the centre of a wrapper. Brush the edge with alittle water, fold in half and bring the two folded corners together; press firmly. Put on a tray dusted with cornflour.
Bring a saucepan of water to the boil. Cook the won tons, covered, for 5–6 minutes, until they rise to the surface. Remove with a slotted spoon and divide among six bowls.
Put the stock in a saucepan with the remaining soy sauce, rice wine, sesame oil and 1teaspoon salt, and bring to the boil. Pour the stock over the won tons and sprinkle with the spring onion.