To begin, peel and cut the potatoes into chunks. Boil in salted water until soft, around 20 minutes. Drain well and mash until smooth. Spread out to cool slightly to remove excess steam. Transition to preparing the dough.

Combine cooled mashed potatoes with flour, egg, butter, and a pinch of salt. Knead lightly until a soft dough forms. Avoid overworking to keep it tender. Move to shaping.

Wash the plums and remove the stones by making a small slit. Place a sugar cube (or 1 tsp sugar) inside each plum along with a pinch of cinnamon. Set aside while preparing the dumplings.

On a floured surface, roll the dough into a log and cut into 12 equal pieces. Flatten each piece into a small disc, ensuring the centre is slightly thicker to hold the plum. Continue with filling.

Place a plum in the centre of each dough disc. Carefully fold the dough around it, sealing tightly. Roll gently between your palms to shape into a smooth dumpling. Transition to boiling.

Bring a large pot of salted water to a gentle boil. Drop dumplings in carefully, stirring once to prevent sticking. Cook until they rise to the surface, about 10 minutes. Lift with a slotted spoon. Move to coating.

In a large pan, melt butter and add breadcrumbs. Stir until golden and fragrant. Add sugar and mix well. This will coat the dumplings with sweetness and crunch. Prepare to coat the dumplings.

Roll each cooked dumpling in the buttered breadcrumb mixture until evenly covered. Work gently to avoid tearing. Transition to final garnishing.

Serve the dumplings immediately, sprinkled with extra cinnamon and a dollop of sour cream if desired. Presentation tip: Place on a rustic platter for a homely feel, letting the golden crumb contrast with the plum centre.