Line a fluted 24cm (9½ inch) tart tin with the pastry. Chill at least 2 hours.
Preheat oven to 180°C.
Bake blind for 15 minutes. Remove baking blind material and bake for further 5-8 minutes until pastry is slightly brown.
Turn oven grill to 220°C. Cut plums in half and remove stones using small paring knife. Bunch halves together cut side up on a chopping board and sprinkle heavily with sugar.
Transfer sugared plums to baking paper lined baking tray. Grill for 5-6 minutes until sugar bubbles and caramelises.
Switch oven back to bake at 150°C. Place plum halves evenly into tart case cut side down.