01 - In a large bowl, mash the cooked potatoes until smooth. Allow to cool slightly.
02 - Add the flour, egg, salt, and sugar to the potatoes and mix until a smooth dough forms. If the dough is too sticky, add a bit more flour.
03 - On a floured surface, roll out the dough to about 1 cm thickness. Cut into squares, approximately 10 cm each.
04 - Place a plum half in the center of each square, sprinkle with sugar and cinnamon (if using), then fold the dough over to encase the plum. Pinch the edges to seal.
05 - Bring a large pot of salted water to a boil. Carefully drop the dumplings into the boiling water and cook for about 8-10 minutes, or until they float to the surface.
06 - In a skillet, melt the butter and add the breadcrumbs. Toast until golden brown.
07 - Once cooked, remove the dumplings from the water and let them cool slightly. Roll the dumplings in the toasted breadcrumbs and serve chilled, dusted with powdered sugar.