Remove the outermost leaves of the lemongrass, bruise the core and cut into pieces approx. 5 cm long. Bring the stock to the boil in a pan, add the lemongrass, kaffir lime leaves, galangal and shallots. Reduce the heat, simmer for approx. 5 mins. Remove the lemongrass, kaffir lime leaves and galangal with a slotted spoon.
Cook the rice noodles according to the packet instructions, rinse with cold water, drain, cover and set aside.
Tom kha gai
Add the palm sugar and coconut milk to the stock, stir until the sugar has dissolved. Add the mushrooms, chilli, tomatoes and chicken, leave the soup to infuse at just below the boil for approx. 10 mins. Pour in the lime juice, season with soy sauce. Add the reserved rice noodles to the soup.
Pour the soup into bowls, garnish with the spring onion and coriander.