1. Shell and devein prawns and wash them thoroughly.
2. Reserve shells. Peel spring onion and coarsely chop.
3. Wash and slice fresh mushrooms.
4. Peel and slice ginger.
5. Wash and roughly chop lemon grass.
6. Wash kafir lime leaves.
7. Wash and roughly chop green chillies.
8. Wash and cut fresh red chilli into slivers.
9. Reserve for garnish.
10. Wash and coarsely chop fresh coriander leaves.
11. Stir in prawn shells, sliced ginger, chopped green chillies, chopped lemon grass, lemon rind and kafir lime leaves in chicken stock.
12. Bring it to a boil, cover, reduce heat and simmer for fifteen minutes.
13. Strain the mixutre through a sieve and return and the liquid to the saucepan.
14. Bring it to a boil.
15. Add prawns and sliced mushrooms.
16. Simmer for two to three minutes and stir in fish sauce and lemon juice.
17. Add salt to taste, stir and immediately remove from heat to prevent overcooking of prawns.
18. Serve piping hot, garnished with silvers of fresh chillies, chopped coriander leaves & spring onion.