To make 4 jars of jam you will need:
500 g jam sugar
Cut the flesh of the watermelon into small pieces. Sprinkle a bit of sugar over these and wait a couple of hours so the watermelon can absorb it. Collect the juice in a bowl and bring this to the boil. Let it thicken a bit and then add the sugar and the melon pieces. Keep stirring well to make sure it doesn’t burn. Once the jam has the right consistency pour it into the sterile jars. Turn the jars upside down for a minute and then back upright again. Allow the jam to cool and store the jars in a cool, dark place.