Finely chop the galangal, the ginger, shallots, three of the chillies, six of the lime leaves and two of the lemongrass stalks (the remainder are for garnish).
Bring the coconut milk to the boil. Stir in the chopped herbs and the lime zest, add the stock and fish sauce and return to the boil. Add the chicken thighs and reduce heat to low. Simmer gently for about 20 minutes, or until the chicken is cooked. Remove the chicken and set aside to cool.
Strain the soup through a fine sieve and discard the solids. Clean the pan and return the soup to it. Add the lime juice, taste and adjust the seasoning if necessary. Slice the remaining chillies, lemongrass and lime leaves.
To serve: shred the chicken, discarding bones and skin, and pile the meat into each bowl. Ladle over the soup and garnish with the slices chilli, lemongrass and lime leaves. Sprinkle over the basil and coriander. ENJOY!