1kg/2¼lb blackberries, fresh or frozen (defrosted if frozen)
1kg/2¼lb cooking apples, quartered, cored and peeled
1.5kg/3lb 2oz granulated sugar
Juice of 1 lemon
Small knob of butter, about 7g/¼oz
1. Add half the blackberries to a preserving pan or the largest saucepan you have. Cut the apples into pieces about the size of the blackberries then add to the pan along with the water. Cover and simmer gently for about 15 minutes or until the fruit is tender.
2. Meanwhile, warm the sugar in a roasting tin in an oven set to 110ºC, 225ºF, Gas ¼. Add the heated sugar along with the lemon juice and the remaining blackberries to the pan and heat gently, stirring occasionally, until the sugar has dissolved.
3. Stand 6 well-washed and dried jam jars and their metal lids in a roasting tin and warm in the oven while the jam is cooking.
4. Increase the heat and boil the jam for about 15 minutes until it becomes thick and falls slowly from a wooden spoon. Alternatively, place a dollop on a chilled saucer then draw a fingertip through – if it wrinkles, the jam is ready.
5. Take the jam off the heat, stir in the butter to reduce any scum, then ladle into the warm jars, filling to the very top. Add a screw-topped lid and leave to cool before labelling.