Preheat oven to 400 degrees.
On a floured surface roll the thawed puff pastry big enough to fit the tart pan.
Lay the pastry into the pan and trim edges.
Put the sugar in a bowl and split the vanilla bean and scrape the seeds into the sugar. Mix to combine.
Sprinkle the desired amount of the vanilla sugar into the bottom of the tart.
Slice the plums into thin slices. Arrange the slices cut side down so they are overlapping.
Sprinkle the rest of the vanilla sugar over the plums.
Bake for approximately 20 minutes until the pastry is golden and the plums are baked through.