Preheat oven to 375 degrees.

Coat the 9 inch cake pan with 4 tbsp butter (the sides as well).

Sprinkle 1/3 cup sugar on top of the butter.

Arrange the plums tightly in the pan.

Pour 2 tbsp melted butter on top of the plums.

Sprinkle the remaining 1/3 cup sugar on top of the plums.

Place the cake pan on top of a sheet pan (just in case the juices spill over).

Put the pan in the oven and bake for 15 minutes.

While the plums are in the oven, cut the puff pastry into a circle slightly larger than the diameter of the cake pan.

Place the pastry on top of the plums. Tuck in the edges.

Cut a few slits into the pastry so that the steam can escape.

Put the pan back in the oven and bake for 40 minutes or until the pastry is a golden brown. Check it at 30 minutes.

Allow the tart to cool for 15 minutes before flipping the tart. The syrup/caramel needs time to thicken.

Put a serving plate on top of the cake pan and carefully and quickly flip it over. Slowly lift off the cake pan.

Serve warm or room temperature with or without vanilla ice cream.