Heat the oil in a pan over a medium heat. Add the lemongrass, coriander roots, prawn heads and shells and chilli and fry for a few minutes, to release their flavour.
Carefully add enough boiling water to cover the ingredients in the pan (CAUTION: there may be hot oil splashes) and simmer gently for 8-10 minutes. Strain the stock and return the liquid to the pan.
Add the shelled prawns, rice noodles and Chinese leaves to the stock and simmer for 3-4 minutes, until the prawns are cooked through.
Stir in the honey and lime juice and continue to simmer for a further minute.
Transfer the broth to a bowl and serve immediately.