Cut the plums lengthwise, but not all the way through, just enough to remove the pits.
Add 2 tablespoons of sugar to them together with one teaspoon of cinnamon, toss well, and set aside.
In a pan set over a low heat, melt the butter, add the breadcrumbs, and stir well then add the remaining sugar and cinnamon, and stir again for a further 2-3 minutes.
Remove fromt the heat and set aside.
Peel and cut the potatoes into fries, and transfer them to a pan set over a medium to high heat.
Cover them with water, and leave to boil until the potatoes are tender.
Drain the water, and mash them potatoes.
Leave to cool, then add the eggs and flour, and knead into a smooth, but very sticky dough.
Take one-two tablespoons of dough, flatten it up, then place a plum in the middle and wrap the dough around it.
Repeat with the remaining plums.
Bring a pot of salted water to the boil, drop the dumplings in, working in batches if necessary, and boil until the dumplings float to the surface.
Remove them from the pot, and toss well into the breadcrumbs while they are still hot.
Leave to cool before serving.