Add the stock, cream, lime leaves, lemongrass, and galangal into a heavy pot and bring to a very low simmer for ten to twenty minutes to let the herbs infuse the liquid. The herbs may optionally be put in an herb bag for easy removal.
Add the chicken and mushrooms and simmer on low, stirring gently, until chicken is cooked.
Add the chillies and remove from heat, stirring gently for a few minutes.
Add lime juice and fish sauce to taste.
Stir in cilantro leaves and serve.