Wash, remove shell and de-vein the prawns retaining their tails. Pat prawns thoroughly dry with an absorbent paper.
Mix garlic paste, oyster sauce, lemon juice, soy sauce, white pepper powder, red chilli flakes and salt in a small bowl. Apply this mixture liberally on the prawns and leave aside to marinate for ten minutes, preferably in a refrigerator.
Mix half cup refined flour, cornflour, baking powder, salt and three-fourth cup chilled water. Whisk thoroughly to make a batter of pouring consistency and set aside for fifteen to twenty minutes.
Heat sufficient oil in a wok.
Spread the remaining flour on a plate, add salt and mix well. Coat the prawns with the flour-salt mixture and then dip in the batter, holding by the tail. Slide them into hot oil gently and deep-fry on medium heat, turning frequently, for two to three minutes or until crisp and golden. Drain on absorbent paper.
To make the dipping sauce, mix soy sauce, lemon juice, salt and chilli sauce well in a small bowl.
Arrange the fried prawns on a serving plate and serve hot with the dipping sauce.