Put the coconut milk and chicken stock in a pot and bring to a simmer. 2. Add the lemongrass, galangal, shallots, kaffir lime leaves and bird’s eye chillies and continue to simmer for a few minutes. 3. Season with the salt, sugar, fish sauce and fresh lime juice. Add the sliced chicken and mushrooms. 4. Total cooking time should not take more than 8 minutes, but always check that the chicken is cooked. 5. Add the coriander and chilli oil and serve.