Preheat the oven to 180°C. Pat dry duck breasts, score skin in a crisscross pattern and lightly season the skin with salt. Place in preheated pan skin side down, using no oil, for 5 mins or until the skin is golden. Turn and cook for a further 2 mins.
Remove pan from heat and place in preheated oven for a further 8-10 mins to your liking. Rest for 5 mins before slicing.
To make the sauce, place the wine, canned plums and ½ cup juice, allspice, Dijon mustard and orange juice in a medium saucepan. Bring to boil, then reduce heat to low and simmer for 10 minutes.
Combine the corn-starch in a bowl with 2 Tbsp of sauce to form a paste and then stir into the remaining sauce. Reduce heat to low and simmer for 2-3 minutes. Pour sauce over duck before serving.