1. Pour the water into a pot, add the lemon grass and kaffir-lime leaves and heat it.
2. Add the shrimps when the water is boiling and cover the pot.
3. Wait for 3 minutes before adding the mushrooms and salt.
4. Leave it to simmer for a few minutes. Then remove from the heat.
5. Season with fish sauce, lime juice and ground chilli.
6. Put the chopped coriander leaves in the pot before serving.