Pit the plums by removing the stones carefully, trying not to break the fruit.
In a bowl, mix the all-purpose flour, a pinch of salt, and a little water to form a soft, pliable dough.
Divide the dough into as many parts as there are plums, flatten each part and wrap it around a plum.
Bring a pot of salted water to a boil and gently place the dumplings into the boiling water. Cook until they float to the surface, about 10-15 minutes.
Meanwhile, in a pan, melt the butter and add the breadcrumbs. Toast them until golden brown.
Remove the dumplings from the pot and roll them in the toasted breadcrumbs, then sprinkle with sugar before serving.