Wash, stalk and stone the cherries. Weigh 750 g fruit. Mix with jam sugar in a large pot and leave to stand for about 3 hours
Wash lemon hot and dab dry. Finely grate the peel. Squeeze the juice. Select the raspberries and wash them carefully if necessary
Add the raspberries, lemon zest and juice to the cherries. Bring everything to the boil while stirring, then boil for exactly 4 minutes
Fill jam immediately into prepared jars and close them. Leave to cool