After much trial and error (and plum puree) I found the best way is to cut your plums into segments first (or halves if you prefer).I make a sugar syrup first and thicken it - which you can do with either cornflour or arrowroot. Then remove from heat, scrape the seeds from a vanilla pod in to it, and leave the pod to infuse for ½ an hour.
Then re-heat thickened syrup, cut plums (firm ones are better - less likely to puree) and drop them in to the syrup and cook for around 5 minutes. Keep checking them - they overcook to a puree very easily. It is best to take them off the heat before they are cooked, as they carry on cooking while they cool down. Place in to large roasting tray to cool - the more more surface area they are in the quicker they will cool/ stop cooking.
Ideal served with panna cotta.
