Score the skin of the duck breasts, rub with five-spice powder and set aside.
Half and de-stone the plums and set aside. Put the sugar, 300ml of water, peeled and sliced ginger, and star anise into a saucepan and bring to the boil and simmer for 5 minutes, then add the plums and simmer for a further 5 minutes or until just tender. Then take off the heat.
Put another frying pan on a very low heat. Season the duck breasts and place skin-side down in the pan. Cook slowly for about 15 minutes, periodically draining off the fat into a bowl.
This slow cooking is to render the fat from the skin, so don't worry that the duck isn't browning off. After the 15 minutes is up, turn up the heat to now brown off the skin-side then turn the breasts over and cook on the flesh-side for a few minutes to brown. Remove from the pan and leave to rest for 10 minutes.
While resting the duck you can stir fry the bok choi 4-5 minutes in a hot wok with the sesame oil and soy sauce, you don't want to over cook them. Then take them out and place one bok choi on each plate, slice the duck breast and also add to the plate along with a spoonful of plums.
Serve with some boiled rice.