Remove the chicken breasts from the bones. Chop the bones into more manageble pieces. Reserve the bones and the skin. Cut the meat into a medium diceseason with salt and reserve.
In a medium sized pot over medium heat, add the butter. When it's melted, add the onion, galangal, curry paste, and reserved chicken bones and skn. Stir and cook to sweat the onions and cook the chicken bones, 5 to 10 minutes.
Add the chicken stock, followed by 2 Kaffir lime leaves, half the bunch of cilantro, garlic, the 2 bruised chilies, and lemongrass. Bring to a simmer and cook gently for 30 minutes or so. Strain the mixture into a clean pot.
Return the broth to the stove over medium high heat. Add the coconut milk, mushrooms, reserved chicken breast, a tablespoon of lime juice, and a tablespoon of fish sauce. Bring to a simmer and cook until the chicken is cooked through, about five minutes or so. Taste and adjust the seasoning as desired with more lemon, fish sauce and salt if it needs it (remember that fish sauce is salty).
Divide into four bowls. Garnish with cilantro leaves, scallion, chilies, and a lime leaf.