For the Knödel (dumplings):
For the dumplings:
- Peel, cook, and mash the potatoes. Put 8 Zwieback toasts into a plastic bag and crumble into small pieces with a rolling pin. Mix together the Zwieback crumbs, melted butter, flour, egg and mashed potatoes. Season with salt and knead into firm dough.
- Roll the dough about 1/4 inch thick onto a well-floured surface. Using a glass, cut 12 round circles. Put half a plum and/or German plum butter into the middle of each circle and form into a dumpling. Dust the dumplings again with flour and put them into boiling salted water. The dumplings are done when they rise to the top.
For the crunchy topping:
- Crumble another 5 Zwieback toasts by the same method. Heat the butter and sauté the Zwieback crumbs until golden brown. Mix together the sugar, cinnamon and Zwieback crumbs in large bowl, While still warm, roll the well-drained dumplings in the mix until they are thoroughly covered. Serve on a warm plate with remaining plums and vanilla sauce.