Peel and de-vein the prawns if necessary and set aside, reserving the heads for later.
Roughly chop the galangal, lemongrass, 1 of the chillies, the garlic and lime leaves. Pick the leaves from the coriander and set aside, then chop the stalk.
In a large heavy-based pan, fry these ingredients together in the peanut oil along with the prawn heads for 5 minutes, then add the chicken stock and coconut milk. Simmer for 10 minutes. Then add the shrimp paste, a few splashes of fish sauce and half the palm sugar. Simmer for a further 2 minutes then pass the liquid through a sieve. Pour the broth back into the pan, add the prawns and cook for 5 minutes.
Cook the noodles in boiling water for 2 minutes, then refresh under cold water and drain.
De-seed and finely chop the other chilli. Zest and juice the lime.
In a bowl mix together the remaining fish sauce, the palm sugar, lime zest and juice, the chilli and coriander leaves. Toss the noodles into the bowl and mix well before topping with the prawns and the sauce.
«You could replace the prawns with different seafoods such as oysters or mussels.»