For the plum dumplings, cook the potatoes, peel and press through a press while still warm.
Mix with liquid egg yolk, flour, butter, a pinch of salt and semolina to a firm dough. Let the dough rest for a few minutes, then make a cooking test and add a little flour as needed.
Pit the plums and replace the pit with a piece of sugar cube.
Form dough into balls the size of plums, flatten them, wrap the plums in them and twist them into dumplings. Place the dumplings in boiling water and cook for just under 10 minutes.
In the meantime, melt butter, add breadcrumbs and sweeten with sugar.
Remove the dumplings from the water, drain, arrange and sprinkle with the butter crumbs.