Preparation:

Boil potatoes with skin for about an hour. Peel and mash them with a potato ricer on a working surface or plate and leave to cool. Then add the sifted flour, the egg and 30 g butter and mix until you obtain a homogeneous, slightly sticky mixture. Roll out the dough with a rolling pin. Use a cookie cutter or a glass to cut the dough into circles (1 cm thick and 6 cm diameter). Put the plums - without pits - in the middle of the dough circle with a pinch of sugar. Wrap the dough around it to form a little ball. Cook them in boiling water and poach until they float back up to the surface.
In another pan, melt the butter, add the breadcrumbs and sauté with the gnocchi.
Serve warm with a sprinkle of sugar and cinnamon.