Cook the chopped flesh of the cooking apple with 4tbsp water until soft.
Put this into a large pan with the blackberries, sugar and 320ml (12fl oz) red wine.
Bring your fruit, water and sugar mixture to the boil, stirring to help the sugar melt, then boil hard until the setting point is reached (105C/220F on a kitchen thermometer).
Skim the surface, then add the remaining 30ml (1fl oz) red wine.
Pot while still hot in warm, sterilised jars.