Wash, dry and pit the cherries. Put them into a large saucepan with
Put the hot jam into clean sterilised jars and tightly close the lids. Put the jars upright into a large saucepan, cover with cold water and bring to the boil. Boil for 20 minutes, remove from the heat and leave the jars to cool in the water before removing them. Check the lid to ensure that a vacuum has been created. Alternatively, tightly close the lids and turn the jars upside down. Cover with a tea towel and leave to cool. Check that a vacuum has been created on the lid.
Store upright in a cool dark place. The jam is ready to be eaten immediately, but will store for months. Once opened, keep in the refrigerator.