Place whole mandarins (skin and all!) and lemon juice in a pot and barely cover with water. Bring to the boil and simmer till mandarins are tender and soft to the touch.
Remove mandarins from liquid and process in a food processor. Give them a few whizzes in the food processor but don’t let it all go mushy. We’re looking for a little texture here.
Return the fruit to the pot and add the sugar, vanilla bean and the mastic. Bring back to the boil, stirring to dissolve the sugar.
Boil the mandarin jam mixture for about 30 mins – the seeds will rise to the surface during this time, and will be easy to remove
Let the mixture cool and store in sterilised jars.