Tom Yum Goong

Peel the prawns, reserving the heads and shells. Slit each prawn down the back and remove its vein. Wash them and set aside. In a large saucepan, heat the oil and add the prawn heads and shells. Cook for 10min, stirring until deep orange. Add the water, bring it to the boil and skim. Add the curry paste and simmer for 20min. Strain the stock and return it to the pan. Add the tamarind, turmeric, chillies, lime leaves and cook for 2 min. Add the prawns for 5 minutes, until pink. Finish with the fish sauce, lime juice and sugar. Serve in bowls garnished with the coriander.