1.In a pot, bring to the boil the chicken stock, kaffir lime leaves and lemon grass.
2.Allow the stock with the herbs to boil for one minute to allow herbs to impart their scent to the stock. Add fresh mushrooms and boil until done (one minute).
3.While the liquid is still boiling add the prawns and season with fish sauce and lime juice. Garnish with bird's eye chili peppers and coriander leaves, serve immediately. Do not over cook the prawns once the prawns turn while, turn off the heat