Sweet and sour soup with prawns

1 pint chicken stock
50g button mushrooms, quartered10 king prawns, remove the head and
part of the shell, leaving the tail on
1 stalk of lemongrass, bruised and sliced diagonally
4 slices galingale, thinly sliced2 kaffir lime leaves
2 medium size green chillies, sliced but do not remove seeds
2 tablespoons of bottled Thai fish sauce
2-21/2 tablespoons lime juice
6 sprigs fresh coriander

Bring the stock to the boil, then add lemongrass, galingale and kaffir lime leaves. Simmer and leave to infuse for 5-8 minutes.

Add the prawns, mushrooms and chillies. Simmer for three minutes.

Add bottled Thai fish sauce and lime juice. Serve garnished with coriander.