To make the filling, mix the egg, sherry, salt, pepper, oil, sugar and cornflour in a bowl.
Mix in the prawns and water chestnuts.
Place 1/2 tspn filling in the centre of each wonton wrapping.
Moisten the edges with water and fold into a triangle and seal.
Heat the stock and keep it warm in a covered soup tureen.
Bring a large saucepan of water to the boil.
Add the wonton a few at a time, and cook until they float to the surface.
Transfer to the hot stock with a slotted spoon.