Wash, halve and stone the plums. Weigh 900 g fruit flesh and cut into large pieces
Mix fruit, jam sugar and almonds well in a large pot. Bring everything to the boil while stirring over high heat. Cook for at least 3 minutes while stirring until bubbly
Immediately fill jam to the brim into prepared twist-off jars. Seal and let cool upside down
Shelf life 6-9 months