Put the cherries (either pitted, whole or halved) into a saucepan and cover with 500ml/18fl oz water. Bring to the boil, then cook until the cherries are very tender and the water almost evaporated.
Peel and grate the Bramley apples, minus the core and pips, and add the grated apple to the pan. Boil again until the apple threads are very soft and falling apart and the liquid has almost disappeared.
Add the sugar and lemon juice, bring to the boil and cook until the preserve reaches 105C/220C on a sugar thermometer. Stir in the hazelnuts towards the end of cooking.
Leave to cool for a few minutes, then pour into hot clean jars and seal immediately.
Leave the jam until the following day before eating, and after opening keep in the refrigerator.