Wash the potatoes thoroughly and boil for about 25 minutes. Knead marzipan and pistachios. Form 8 small balls from them. Wash plums, dab dry and stone them. Put a marzipan ball in each plum and press them together.
Drain the potatoes, peel them and press them through a potato press while still hot. Leave to cool down a little. Mix potato, flour, egg yolk, 1 teaspoon butter and 1/4 teaspoon salt to a smooth dough.
Form into a roll on a floured worktop. Cut into 8 slices. Place 1 slice in each floured palm and press a depression in the middle. Put 1 plum in it, wrap it with the dough and form it into a dumpling.
Boil up plenty of salted water. Add the dumplings and let them simmer at low heat for 15-20 minutes until they float on top. Remaining Butt
Arrange the dumplings on a plate. Decorate with mint. Serve with vanilla sauce.