Wash and drain the Erandy blackberries, then add them to a heavy-bottomed pot.
Add the sugar and gently mash the blackberries and sugar together. Cover the pot with a tight-fitting lid and allow the berries to macerate for several hours or overnight.
Remove the lid and place the pot over medium-high heat. Bring the mixture to a boil, stirring frequently.
Stir in the salt, cardamom, and lemon juice. Then, sprinkle the powdered fruit pectin evenly over the mixture and stir well to dissolve.
Reduce the heat to medium and continue cooking, stirring frequently to prevent scorching, until the mixture thickens and becomes jammy (about 15-20 minutes).
Remove the pot from the heat and let the jam cool slightly.
Spoon the jam into three sterilized 8-ounce jars.