Wash the plums thoroughly and soak them in a saltwater solution.

Use a knife to score around the plums.

Add sugar to the plums to marinate, and wait until the sugar dissolves, about 5 hours.

Put the mixture in a pot and bring to a boil over medium heat. Since plums are acidic, use a clay or glass pot to avoid harmful reactions with metal pots.

Avoid stirring too much with a spoon to prevent the plums from breaking apart. Cook until the liquid is almost evaporated.

Strain the mixture to separate the syrup, and dry the remaining plums by sun-drying or using a fan.

Place the plum jam on a tray lined with parchment paper. Dry the plum jam at 250°F (120°C) for about 1 hour or sun-dry for one day.