Put the flour, powdered sugar, butter (crushed with a knife) and egg yolk in a large bowl and knead everything quickly to form a dough.
Spread the batter in the springform pan. There may be a bit of batter left over. But better a little more than too little. Finally, distribute the plums on the dough. It is best to stand up so that there is plenty of room for plums on the cake, but keep 6-8 plums.
Bake the cake in the oven at 160 ° C for 50 minutes.
While the cake is baking, bring the remaining plums to the boil with water in a saucepan. The plums should just be covered with water. Add about 1 tablespoon of preserving sugar per plum. When the plums are nice and mushy, use a hand blender to grind everything until you have a nice, sticky plum juice.
Drizzle the cake with it after baking. Then put the cake in the refrigerator for at least 4 hours.