Heat a cupful of coconut cream (scooped off the top of the milk, after it has been left to stand for a while) in a large heavy saucepan, stirring occasionally, until the creamthickens and oil bubbles around. By this time it should be reduced to a quarter of the original amount.
Add the curry paste and fry the rich oily cream for about 5 minutes, stirring constantly. The curry paste will smell cooked, and the oil will separate from it when it is ready.
When this happens add the pieces of chicken and cook over a medium low heat, stirring frequently and turning them, for about 15 minutes. The chicken will change color and have a cooked appearance.
Add the remaining coconut milk, citrus leaves, salt and fish sauce and stir while the coconut milk comes to the boil.
Then turn the heat down and allow to simmer uncovered for about 35 to 40 minutes, or until the chicken is well cooked and tender and the gravy is rich.