1kg plums, halved with stones removed
1/4 cup French Lavender flowers, rinsed (or other edible lavender varietal i.e. Lavendula angustifolia, which also may be sold as Lavendula officianalis, Lavendula vera or True English Lavender)
1kg Chelsea Jam Setting Sugar
10g butter

Place plums and lavender flowers in a food processor and process to a chunky puree. Transfer mixture to a preserving pan or large heavy-based saucepan.
Add Chelsea Jam Setting Sugar and stir over heat until dissolved. Do not boil at this stage. Add butter, increase heat and boil for 4 minutes or until settling point is reached. Test by spooning a little jam onto a chilled saucer. Run your finger through the jam and if it wrinkles then it's ready. If jam doesn't wrinkle then boil for another 2 minutes and test again. Retest at 2 minute intervals until settling point is reached.
Remove pan from heat and skim off any foam from surface.
Spoon into sterilised jars and seal well.