We prepare the dough as follows: in a bowl we put all the ingredients and mix them well until we obtain a compact dough. We wrap it in foil and put it in the fridge for 30-45 minutes. It goes on and on from one day to the next (that's what I did).
Sprinkle the flour on the work surface and spread the dough in a thin layer, a few millimeters and place it in the tray lined with butter and flour, climbing it on the walls of the bowl. I used a tray with a diameter of 26 cm.
We keep the rest of the dough to decorate the tart.
Bake the dough for 15 minutes in the preheated oven.
Remove from the oven and sprinkle 1-2 tablespoons of grated semolina (to absorb moisture from the plums).
The plums, washed well, cut them in half and remove the seeds. Then cut the halves into 3-4 slices, mix them with the sugar and put them on the fire for about 15 minutes, stirring from time to time.
Mix the starch with 4-5 tablespoons of the plum juice and pour it over the plum mixture.
Pour the warm plum composition over the pre-baked dough; on top decorate with the remaining dough and grease with 1 egg.
Put the tray in the oven for about 20 minutes.
After removing the tart from the oven, it is good to keep it covered so that it does not harden. After 10-15 minutes, when it has cooled a bit, I put it in a cake holder with a lid (it goes and covered with a kitchen towel).