For the plum dumplings, cook the potatoes the day before. Press the curd vigorously through a tea towel to drain it. Spread the squeezed curd cheese in small crumbs, e.g. on a baking tray and let it dry in a clean place until the next day.
The next day, grate the potatoes into a suitable bowl, mix with the egg and half a teaspoon of salt and add enough flour to make a dough that is easy and soft to knead.
Slit washed plums lengthwise, remove seeds and fold them back up filled with a sugar cube.
Shape the dough into balls and flatten to make patties about 1 cm thick. Place a filled plum in the center and press the dough around the plums to form dumplings.
Cook in lightly boiling water for about 20 minutes. The dumplings are ready when they float on the surface.
Form the dried curd into a firm ball and carefully brown the butter. Remove the dumplings from the water with a slotted spoon and serve on a preheated platter.
On the plate, divide the dumplings with a fork, sprinkle with sugar, grate some of the dried curd over the plum dumplings with a grater without pressure and drizzle with brown butter.