When Grandma cooks jam, she will make her choice of fruit dependent on what special fruits are in season, the lushest offers at the farmer’s market, and on cases of uncontrollable fruit abundance in the neighbours’ gardens. She quickly cooks 2 or 3 jars between her usual cooking, gardening and housework.  The black fruit jam however is one of her true classics.
The fruit/ sugar ratio is always the same: fruit to sugar, 2:1.  The rest is stirring. First hot, while simmering, then cold to enjoy the reliable process of thickening.