Put all the ingredients for the dough in a suitable bowl and mix with a mixer or food processor for 5 minutes until smooth. Preheat the oven to 50 degrees for 5 min, turn it off and let the covered dough rise in the oven. Cut the plums in half and remove the seeds. Form a piece of sugar cube in each plum. Form dough into a roll (0 3 cm), cut even pieces of dough into small pieces, press a plum into each, form into a dumpling and cook in salted water on automatic heat 4-5. Dumplings are ready when they rise to the surface.
Remove dumplings, tear open with two forks, pour liquid butter over them, sprinkle with sugar and chopped hazelnuts. Serve with vanilla sauce.