Preheat the oven to 170 °C. Wash plums, remove the pits, and place in a large roasting pan with a lid. (Feel free to really fill up the pan!). Sprinkle with sugar, spices, salt, and zest. Slice the vanilla pod and scrape out the pith. Add the pulp and husk to the fruit. Drizzle over vinegar and rum. Roast for five hours. Remove the vanilla pod and cinnamon stick before transferring povidla to sterilized jars. Seal the jars and turn upside down for a few minutes then return to upright position.