Mix 1-2 tsp cinnamon with 2 tbsp sugar. Pit the plums and sprinkle with the cinnamon and sugar mixture.
Peel the potatoes and cook in salty water. The water should just cover the potatoes. Add 1/2 tsp salt. Cook for about 10-15 min or until soft.
Rinse the potatoes and mash them. There mustn't be any lumps. Make a little hole in the middle and add the egg. Fold into the mashed potatoes with a fork. Add the egg yolk and do the same.
Add the flour until you have a dough. Depending on the quality of the potatoes this could be less or more flour. Lastly, add the cornflour. Now you have a dough.
Make a roll and cut it into 12 pieces (about 4 cm each). Form into a ball and knead the balls flat.
Put one plum (halved) in the middle and form into a ball.
Bring a big pot of water to boil and gently put the balls into the salted boiling water. Put in just a few balls at a time and they should float up to surface once they are ready.
Heat up a large pan to medium heat and roast the breadcrumbs. Stir the breadcrumbs until golden brown.
Roll the hot dumplings in the breadcrumbs until covered. Serve with sugar mixed with cinnamon.