This famous soup is known in Thailand as Tom Yum Goong and acts as a piquant balance to the rich coconut flavour of Thai curries. If you want the soup a little less hot, lessen the chillies.
Peel and devein the prawns, keeping the tails intact and reserving the heads and shells. Cover and refrigerate the prawns. Rinse the heads and shells and dry well.
2 Heat the vegetable oil in a wide, shallow pan or wok, then add the prawn shells and heads, lemon grass stalks and ginger and stir-fry over high heat for 3-4 minutes. Add