Wash potatoes and cook them in the shell until tender. Peel them while they are still hot, mash them into a puree with butter and salt (be sure there is no lumps left). Leave it to cool to room temperature.

When potato puree is cooled, add 1 egg and flour. Sprinkle work surface with some flour and knead the dough until smooth (add more flour if the dough is too sticky).

Cut the dough into 20 equally sized pieces/balls.

In a small bowl mix sugar and cinnamon.

Wash plums, cut them in half if they are big ( if you use small plums, no need to deseed them-this way you will keep juices inside) and roll each plum into sugar and cinnamon mixture. Take each piece pf dough and gently flatten it in your hand. Please plum into the center of each dough round, enclose it completely, and roll it into a ball.

Drop dumplings in the boiling water and cook at a simmer for around 15 minutes (when dumplings rise to surface cook them 2-3 more minutes).

While dumplings are cooking melt the butter in a saucepan over low heat, add breadcrumbs, and allow them to brown a little.

In a small serving bowl combine sour cream, vanilla extract, and sugar and stir to dissolve. Set aside.

Drain cooked dumplings, roll each one into buttered breadcrumbs.

To serve, sprinkle wit some sour cream and sugar mixture.