How to make
Pour half the sugar into a saucepan, cover it with the cleaned blackberries, sprinkle the rest of the sugar on top and put it in a cool place for 12 hours.
Pour in 6.8 fl oz (200 ml) of water, shake the pot, cook over a moderate heat, by stirring to prevent burning, and when the jam is done, stir it and remove the foam that forms.
Cover the container with a clean and damp cloth and let the jam stand for 10-12 hours, then pour it into jars that close tightly. You can weld them.
