How to make
Combine the flour, sugar, butter and salt and knead them with your hand until you get coarse crumbs. To make it easier, you can use a blender. Add the egg to the crumbs and knead a smooth dough. Form a ball, wrap it in aluminum foil and leave it in the fridge for half an hour.
In the meantime, wash and dry the plums. Cut them in half and remove the pits, cutting each half in 2 if desired. Mix the plums well with the crystal sugar for the filling and the cinnamon.
Lay out the prepared dough into a crust that covers the sides of the form you intend to bake in. Be sure to butter the form and sprinkle it with some breadcrumbs before you actually place the crust.
Transfer the crust in it, using a rolling pin to help you, and press down on it lightly so it sticks to the sides firmly. Cut off the edges that are sticking out and sprinkle the dough with the remaining breadcrumbs.
Arrange the plums on top as shown (see photo). Put the pie to bake in a preheated 360°F (180 °C) oven for about 35-40 min. Mix the powdered sugar with 1 tbsp water, enough to get a thick sugary paste.
Smear the homemade plum pie with the sugary mixture using a brush and let it cool in the form before serving.