Wash and stone the cherries, weigh 500 g cherries. Wash blackberries and possibly sort them. Mix the fruit with jam sugar and genever in a pot. Bring to the boil over a high heat, boil for about 3 minutes while stirring continuously. Immediately pour the jam into 5 preserving jars (approx. 250 ml each), close with preserving rings and lids. Let stand upside down for about 5 minutes.