Tie reserved cherry stones in muslin. Place all ingredients (including stones) in a wide-based saucepan and stir over very low heat until cherries release their juices and sugar is dissolved. Bring to the boil and cook for about 45 minutes or until jam is cooked. (To check, place a small amount on a chilled saucer - it should set.) Remove cherry stones and lemon zest and discard. Spoon jam into hot sterilised jars and seal when cool.

Makes 4-5 cups