1kg fresh rasps
Place raspberries in pan on a low heat to cook very slowly for 20 minutes.
Add the sugar which has been heated in a microwave or oven and stir until it has dissolved completely.
Turn up the heat and boil rapidly for ten minutes – make sure you have a large pan for jam making because it is at this stage you are liable to cover the cooker with bubbled over jam!
Remove from the heat and put some onto a saucer that has been in the freezer for 5 minutes. When the jam is cool push with your finger and if you see a crinkly skin on the surface it has set. If not boil again for 5 minutes and repeat the testing process.
Once set, add a knob of butter to the jam and allow to cool before filling warmed, sterilised jars.