Start by washing and pitting your mirabelle plums.
Place them in a large stewpot, cast-iron casserole or jam pan.
Add the sugar and stir.Cover and leave to stand for 2 hours or even overnight. Then heat, stirring regularly, and cook for around 40 minutes.Remove the scum with a skimmer. While the jam is cooking, wash and sterilize your jars by heating them in gently simmering water.
Once the jam is ready, pour it into the jars, taking care not to burn yourself.Fill to within 1 cm of the rim.Close the jars and turn them upside down until cool. Store jam for a few weeks/months in a dry, dark place.
