1. Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).
2. Combine margarine, flour, sugar, cinnamon, and vanilla extract in a mixing bowl until you have a fine crumb mixture.
3. Add the egg and knead until you have a dough.
4. Combine the plum slices with cinnamon and sugar and set aside.
5. Grease a nine inch round pan or a nice oven-to-table dish.
6. Separate off one cup of dough and set aside for topping, and then roll out the remaining dough between two pieces of Gefen Parchment Paper into a 12-inch round circle.
7. Lift off top piece of parchment paper and turn the dough into the bottom of your pan, arranging it so that it comes up the sides of the pan.
8. Add the plum slices in a circular pattern, creating a flower effect (you will have enough for two layers).
9. Roll out the remaining dough between two pieces of parchment paper into a 10-inch circle.
10. Turn dough onto the plums and smooth carefully, and then fold the bottom layer of dough over the top layer and neatly seal the edges.
11. Brush the top of the tart with water or orange juice and sprinkle a dash of sugar on top, and bake for one hour.