Prawn and Oyster Mushroom Soup

400g green prawns
250g oyster mushrooms
1 tablespoon vegetable oil
1.5 litres water
4 kaffir lime leaves
1 stalk lemongrass
2 small hot chillies
125ml fish sauce
a handful of rice noodles, broken into short lengths, softened in boiling water for three minutes then rinsed and set aside
juice of two or three limes
a few sprigs of Vietnamese mint or fresh coriander

Remove the heads and shells from the prawns and set aside. Devein the prawns, rinse and refrigerate until required. Break up the oyster mushrooms into bite-sized pieces and set aside.

Heat the oil in a deep heavy-based pan then throw in the prawn heads and shells and fry over a medium heat for five minutes, pressing the heads down to release the juices. Do not burn.

Meanwhile peel the tough outer leaves from the lemongrass then bash the stalk with a meat mallet to release the flavour.  Discard the stems from the kaffir lime leaves

Deglaze the pan with half a cup of water then add the remaining water, the fish sauce, the bruised lemongrass and the kaffir lime leaves. Cut a slit in the end of the chillies so they remain whole but release their flavour.

Simmer for 45 minutes until the liquid has reduced a little and the flavours have developed. Check the seasoning, adding a dash more fish sauce if further salt is required.

Remove out the prawn debris and other seasonings with a perforated spoon then line a large sieve with muslin or with a new disposable open-weave kitchen cloth, place it over a bowl and strain the soup.

Clean the pot and pour in the strained broth. Bring to the boil then add the prawns, the oyster mushrooms and the rinsed noodles. Simmer for about three minutes until the prawns are cooked then add the lime juice. Serve in deep bowls, sprinkled with shredded Vietnamese mint or fresh coriander.

Serves two, or four as a soup course.