Remove the apples from the apples and cut the fruits with medium lobules. Cut the plums along in half and take out the bones.
Put sugar in a saucepan and add water. Put on a moderate fire and, stirring, completely dissolve the sugar. Put the apples and plums in a syrup.
Bring the jam to a boil, cook for 10 minutes, remove from heat and leave for 4 hours. In the same way, cook the jam twice more. At the end of the last cooking, add the citric acid, stir and cook for another 5 minutes.
