Wash, peel, core and slice the apples
Wash the blackberries in a colander and shake well.
Stew apples gently in the water until soft
Add the blackberries and the lemon juice and continue simmering until both fruits are soft
Add the sugar and stir over a low heat until dissolved
Boil rapidly for 15 minutes, stirring now and then, until setting point (105 deg C) has been reached
Skim the jam if necessary and then pot and cover immediately (while still hot)