Combine the tomato puree (paste), soy sauce, chilli sauce and sugar together, then pour into a sauceboat. Set aside.

Remove the shells from the prawns or shrimps, leaving the tails intact. Under cold running water, gently remove the black veins from the flesh, then drain on kitchen towels.

Put the beaten egg into a bowl and beat in the flour, cornflour (cornstarch), ginger, salt and water until the mixture forms a smooth batter.

Fill a large saucepan one-third full with oil and heat until it reaches 180°C (350°F) on a deep-fat thermometer, or until a small cube of stale bread dropped into the oil turns golden in 55 seconds. Holding the prawns or shrimps by the tails, dip each one in the batter, then arrange them, a few at a time, in a deep-frying basket. Carefully lower the basket into the oil and fry for 2 to 3 minutes, or until they are golden brown. Remove from the oil and drain the prawns or shrimps on kitchen towels.

Transfer to a serving dish and serve at once, with the sauce.