Marinate the meat: overnight or longer, max. for 2 days. Using a sharp knife, score the skin in a cross-hatch pattern (but not the meat, otherwise it can dry out, scoring the skin makes rendering the fat easier).
Prepare a small bowl (the meat should be almost completely submerged in the marinade, you can also use a thick ziplock bag). Mix the ingredients for the marinade, add the duck breast, skin-side up, cover and put in the fridge.
On the second day: Preheat the oven to 120°C / 250°F.
Sear the meat: remove from the marinade, pat dry thoroughly with kitchen paper. Place on a cold (!) pan, skin-side down, turn on medium heat and cook for about 4 minutes and then 2 minutes on the other side. Skin should be browned and crispy and the fat rendered. Remove excess fat (but reserve it and use to fry potatoes). Leave a teaspoon of fat in the pan.
Bake: put the duck into a small baking dish. I used a 20 cm/8-inch oven-safe pan, the same pan that I used to sear the meat. Pour in the marinade and about ¼ cup of water, the amount of water depends on the size of the dish used (you should have minimum 1.5 cm / ½ inch liquid in the pan). But more water = reducing the sauce takes longer. Cut the plums in half, remove the stones, arrange around the meat. Place the dish in the oven.
Bake in a preheated oven for about 45 minutes or less. After this time the duck should be ‘well-done’, internal temperature should be around 70°C / 160°F. If you prefer your duck breast medium, roast them for about 30 minutes, to 60°C / 140°F. Medium-rare is 52°C / 125 °F . The baking time will depend on how long you’ve seared the meat in the pan and how big your duck breast is. It’s important to cook the meat to temperature not to time, you can measure internal temperature with an instant thermometer. Well-done duck breast (safe for kids to eat) should be cooked to a minimum internal temperature of 71°C / 160°F. After removing the meat from the oven, its internal temperature will continue to rise. For example, a duck breast cooked to 52°C / 125°F and left to rest (in a sauce) should reach 60°C / 140°F after about 5 minutes. Instant thermometer should be sticked into the thickest part of the meat.
Remove the meat from the oven, leave in the sauce and set aside for about 5 minutes.
Prepare the sauce: If the plums are very soft, remove them from the sauce, but leave harder fruits in (very soft plums will fall apart completely while reducing the sauce). Cook the sauce for about 10 minutes over medium heat until thickened. Discard cardamom capsules, star anise and cinnamon stick.
Serve: Cut the duck into slices, pour the sauce over, serve with cooked rice and roasted plums. Optionally, sprinkle with coriander leaves and sesame seeds.
How to cook rice: Add ½ cup of rice into a medium pot, pour in 1 cup of boiling water, season with salt, cover, bring to a boil over low heat. Cook for about 15 minutes or until rice absorbs water and is soft.