Halve the greengages, remove the stones and chop roughly - I chopped each half into 4 or 6 pieces, but you can leave chunkier if you would like larger pieces in your jam
Put the fruit into a large saucepan along with the sugar and water. Remember that jam will bubble and boil as it cooks, so it is better to choose a pan where the contents leave plenty of room for this to occur without the risk of it boiling over
Press down firmly on the cardamom pods using the back of a blunt knife until they crack open. Scoop the pods and seeds into the pan
Slit the vanilla pod lengthways with a sgharpknife. Scrape the seeds into the saucepan then drop in the pod
Add the cinnamon, star anise, ginger and nutmeg to the pan
Stir everything together, then cook over a gentle heat for around 20 minutes until the sugar has dissolved and the fruit is soft
Take off the heat and leave the jam to infuse for 30 minutes
Remove all of the spices - count them out to ensure none are left behind
Optional step: use a stick blender to perform 3 x 1second pulses of the jam. This breaks some of the fruit pieces down and helps create lovely greengage flavour in each spoonful, whilst still leaving plenty of fruity chunks behind
Prepare 2 sterilised jam jars: wash in soapy water, rinse and then put into an oven heated to 140C/ 284F for 15 minutes
While the jars are sterilising, cook the jam over a medium-high heat, stirrringfrequently to avoid burning, until it reaches 105C/ 221F on a digital food thermometer
Once this temperture has been reached turn off the heat, stir the butter through the jam and leave to cool for 10 minutes
Stir before decanting into the prepared jars. Cover each jar with a circle of wax paper and secure the lid tightly. Invert the jars then leave to cool completely before labelling