Wash, drain and stone the plums. Grease the bottom of the pot, put the plums in and simmer with a little water until the juice comes out. Let the juice evaporate until the jam becomes quite thick and stops sticking to the pot. Stir frequently while simmering, preferably with a wooden spoon. At the end of cooking add the sugar. Pour a spoonful of jam on a cold saucer, spread a thin layer and make a furrow with a teaspoon. If the furrow stays, the jam is ready. If the jam is not sufficiently evaporated, the furrow blends disappears. When the jam is done, put it in jars and pasteurise in the oven at 100°C for 10 minutes.
1 kg plums
0.3 kg of sugar