Clean and dry the plums, cut them in half and remove the pit
Cut the ½ vanilla bean lenghtwise
Put the oven to heat on 180°c (hot air)
Place the half plums tightly, standing up, in a circle in the muffin pan. Place two half plums in the middle, one skin down the other skin up.
Meanwhile make your caramel: Starty by melting the sugar over medium heat. It is important to be patient and let it melt completely before you stir it. Once melted, add the butter and the vanilla bean and whisk until butter and sugar have completely blended
Add a spoon of caramel on each plum circle in the muffin pan
Roll out the puff pastry and cut out 6 circles same size, or slightly bigger as the muffin pans (as it shrinks slightly during cooking)
Place the pastry discs on top of the plums and caramel and push it tightly down
Place the pan in the oven and cook for 20-25 minutes, until the pastry is golden brown
Let the tarts cool down in the muffin pans 30-45 mintues
Place a big plate tightly on top of the pan and turn them both around swiftly to let the tarts come out of the pan
Serve still hot together with a spoon of creme fraiche
Notes
If the plums fall out of the side when turning it over, put them delicately back with two forks. The longer it cools down the better it sticks together.