While your oven is pre-heating, prepare your plums by cutting them in half, removing the pits and then set aside.
Grab a tart pan (circular, rectangular or square work fine) and grease it and set aside so it is ready for the pastry crust you will be rolling out. If you do not have a tart pan, a pie dish will work well too but the presentation will not be as pretty.
Now on a lightly floured work surface, roll out your pastry crust until it is just a little bit bigger than your tart pan.
Place your crust inside your pan pressing up along the sides so that it stays in place.
In a medium bowl, mix together your plums, cinnamon, 2 tablespoon of sugar and lemon juice. Once the plums are all mixed in with the spices, place the plums on top of your pie crust cut side up and bake for 15 minutes.
While it is baking, in a medium bowl, whisk together your egg, ⅓ cup of cane sugar , vanilla and cream until it is a pale yellow color.
Remove your tart from the oven and now pour this egg mixture over the top of your plums and pastry and place back in the oven and bake for 20 more minutes until the custard is set and not jiggly anymore and the top is a nice golden color.
Remove from the oven and let rest for 10 minutes on a cooling rack. If you used a tart pan, carefully remove the outer layer of the tart pan and let it cool for another 5 minutes.
Cut your tart into slices, dust with powdered sugar and enjoy!