Mix the flour with the pieces of butter, sugar and salt. Knead together, then add 3 tablespoons of cold water and work to form a smooth dough. Wrap in foil and rest for 1 hour in the refrigerator.
Rinse the plums, cut in half, remove the pits and sprinkle with lemon juice. Place in a bowl and mix with the sugar, cinnamon and cornstarch. Preheat the oven to 200°C (approximately 400°F).
Divide the dough into a slightly larger and a smaller portion and roll flat.
Place the larger portion of the flattened dough in pie pan, forming a high crust; pierce several times with a fork. Pour in the plum mixture and cover loosely with the second sheet of dough. Press the edges together and press down firmly. Cut a hole in the middle of the top crust. Bake for 45 minutes, then sprinkle the hot pie with sugar and serve warm.