To prepare the duck breasts, score the skin with a cross hatch pattern, being careful to avoid cutting deep enough to expose the flesh. Generously season the skin and place in the fridge, skin-side-up, for 30 minutes – 2 hours to dry.
To prepare the plum sauce, add the halved, stoned plums to a medium saucepan with the sugar, red wine, butter, the cinnamon stick, and a pinch of salt. Slowly bring to the boil then simmer uncovered for around 20 minutes, until the plums are soft. Stir occasionally to prevent the plums from sticking.
Place the duck breasts in a cold pan, skin-side-down, and cook over low heat, using a smaller pan or weight to press the duck breasts, exposing more of the skin to the heat. Cook slowly until the fat renders and the skin begins to crisp. This should take around 15 – 20 minutes, depending on the size of the duck breasts. At this point, increase the heat and cook for another 2-3 minutes until the skin is golden brown and crispy.
Turn the breasts over and cook over a medium heat until the flesh is seared, and the internal temperature reaches 120-130F for medium-rare. This will only take up to five minutes. Cook to 155F if you prefer your duck breasts well-done.
Remove the duck from the pan and rest for 15 minutes before slicing. Strain and reserve the fat in a glass jar with a lid. It’ll keep in the fridge for a few good few weeks.