Cut the apples into small chunks.
Put them and 125ml of water into a large saucepan.
Cook with lid on over a medium heat for about 10 to 30 minutes, checking to ensure the apples haven’t gone mushy.
In the last 5 minutes of cooking time, add the blackberries.
Lower the heat and add the sugar and stir without it boiling until the sugar has dissolved.
Bring the jam to the boil for about 20 minutes, stirring often uncovered. Be careful of the jam spitting.
Stir across the base of the pan to ensure it isn’t sticking or burning.
Remove from the heat, and allow to cool before transferring the jam into sterilised jars.
Store in a cool, dark place for 6-12 months.
Refrigerate after opening.