Wash the potatoes and cook in boiling water for about 20 minutes. Drain, peel and press through the potato press while still hot. Leave to cool. In the meantime wash, cut and stone the plums. Knead mashed potatoes, flour and eggs, season with 1 pinch of salt.
Dust hands with flour. Press 1 tablespoon of potato dough flat in your hands, place a plum on top, add 1 piece of sugar and sprinkle with some rum. Close the dough around it and form it into a dumpling. Repeat the process until 16 dumplings are formed. Put raw dumplings on a board dusted with flour. Heat water in a large pot (do not let it boil), salt it and let the dumplings simmer in 2 portions for about 10 minutes. Melt butter in a pan. Roast breadcrumbs in it. Take the dumplings out of the cooking water, let them drain and arrange them on plates. Pour breadcrumbs and butter hot over the dumplings.
Melt butter in a pan. Roast breadcrumbs in it. Take the dumplings out of the cooking water, let them drain and arrange them on plates. Pour breadcrumbs and butter hot over the dumplings. Chop the pistachio kernels and sprinkle over the dumplings. Dust with icing sugar. Serve with vanilla sauce