Cut the plums lengthwise, but not all the way through, just enough to remove the pits.
Add a quarter of a cup of sugar to them together with one tablespoon of cinnamon, toss well, and set aside.
In a pan set over a low heat, melt the butter, add the breadcrumbs, and stir well for 2-3 minutes, then add the remaining sugar and cinnamon, and stir again for a further 2-3 minutes, until the breadcrumbs become golden.
Remove fromt the heat and set aside.
Boil the potatoes, either with their skin on, or peeled and cut into chunks. Once they are tender, drain the water, and mash them well.
Leave to cool, then add the eggs and flour, and knead into a smooth, but 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, 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.