For the medlar jam, peel and core the medlars and add apple juice to 1 kg of fruit mass. Puree finely with a blender and stir in the jelling sugar and lemon juice.
Bring to the boil and simmer for 3-4 minutes until the jam gels (do a jelly test on a plate).
Fill into hot rinsed jars, close and let cool upside down.