How to cook
Cut the watermelons in halves, scoop out the flesh with a spoon, mash it lightly and pass it through a sieve to separate the seeds. Put it in a gauze and drain out the juice.
Pour it in a pot and bring to a boil. Boil 10 min. on low heat, while constantly removing the foam. Remove it from the stove, strain through 2 layers of gauze and put it back in the pot.
Boil on low heat until the volume of the liquid is reduced by 2/3. It will take about 5 hours. The watermelon jam is ready once a drop of it does not run along a cold plate.
Distribute the ready watermelon jam into dry jars, seal them and let cool at room temperature. Store in a cool area away from sunlight.