Bring the stock to the boil and poach the chicken for 15 minutes. Remove and set aside to cool.
Add the galangal, garlic, coriander, lime leaves, lemongrass, spring onions and tomato. Simmer for 15 minutes.
Meanwhile, remove the chicken off the bone and discard the skin. Shred the chicken.
Add the coconut milk, mushrooms, lime juice, fish sauce, chilli and the chicken and simmer for another 10 minutes.
Season to taste with more fish sauce or lime and add coriander just before serving. Recipe reprinted with permission of BitsofCarey. To see more recipes, click here.