Tom Yum Goong

Steps

1. 1
   Peel and devein the prawns, leaving the tails on; keep the heads and shells.
2. 2
   Simmer the heads and shells in the water for 10 minutes, then strain — this quick shell stock gives far more flavour than plain water.
3. 3
   Bruise the lemongrass with the back of a knife and cut it into 4 cm lengths. Bring the stock back to the boil with the lemongrass, galangal, torn lime leaves and chillies and simmer 3 minutes to infuse.
4. 4
   Add the mushrooms and cook 2 minutes.
5. 5
   Stir in the chilli paste, fish sauce and sugar.
6. 6
   Add the prawns and cook only 2 minutes, until pink and just curled — overcooked prawns turn rubbery.
7. 7
   Take off the heat and stir in the lime juice; added off the heat it keeps its fresh sourness, while boiled it turns bitter.
8. 8
   Taste for balance — sour first, then salty, then hot — and serve scattered with the coriander. The lemongrass, galangal and lime leaves stay in the bowl for aroma but are not eaten.