Wash the freshly picked fruit and place in a large saucepan with a little water and the lemon juice. Bring the fruit to a gentle boil. When the fruit is simmering add the apple, cut and cored but not peeled (the peel contain pectin, which will help your jam set) and the sugar. Stir often and cook for 30 minutes, then blend with an immersion blender. Cook for 10 more minutes, at this point the jam should start setting (check by picking up a little with a metal spoon).
Place the hot jam in sterilised jars, dried in the oven. Either seal the jars with cellophane covers (available in all supermarkets) and secure with an elastic band, or use capsule lids (I use Quattro Stagioni brand).
If using capsule lids, seal the jars well, place in a pot and cover with water. Bring to the boil and simmer for 20 to 30 minutes, depending on the size of the jars. Let the jars cool down in the pot overnight and when they are cold make sure that the capsule has popped by pressing gently on the lid. Properly sterilised jars will keep for over a year.