Boil the potatoes until tender eve. Mash it into purée. Add the flour, corn starch, semolina and eggs, knead the dough. Remove from the plum pit, put in its place a sugar cube. Wrap each plum in the batter, cook on low heat in boiling water for about 15 minutes. Melt the butter, mix with sugar and cinnamon, pour the finished dumplings.