For the Rösti, cook the potatoes with skin for about 20 minutes. Drain, quench, peel and let cool.
For the plums, caramelise 150 g sugar in a wide pot. Deglaze with port wine, stir in frozen plums and vanilla sugar. Bring to the boil and simmer covered for about 5 minutes. Then remove the lid and simmer until the plums are soft but not overcooked.
Mix sour cream with 50 g sugar. Beat 3 egg whites until stiff, while pouring in 50 g sugar. Fold the beaten egg whites into the sour cream.
Coarsely grate the potatoes. Roast the flaked almonds in a pan without fat. Knead potatoes, almonds, 1 tablespoon sugar, 1 pinch of cinnamon, 1 pinch of salt, flour and 1 egg.
Heat the clarified butter little by little in a large pan. Fry small, flat Rösti from the potato dough in portions on both sides at medium heat until golden brown. Drain on kitchen paper and serve with the sour cream and port wine plums.