Using a Stand or hand mixer, whisk together the butter, sugar and salt until creamy. Carefully mix in the egg and quark/yoghurt.
At last, add the flour to the bowl and combine it into a homogenous dough. The dough should not be sticky. Add a little more flour if you find it sticks too much to your fingers.
Cover the bowl with a clean tea towel and place it in the fridge to rest for around 30 minutes
In the meantime, combine the sugar and ground cinnamon in a little bowl and mix well.
Wash the plums. Make a lengthwise incision on one side of the prune and remove the stone from the inside. Fill the core of the plums with a teaspoon of cinnamon sugar mixture and set aside.
Once the dough finished resting in the fridge, remove it and divide the dough into 10 equal portions. (The exact quantity will depend on the size of your plums. The plums will not be equally sized. So not worry if your dumplings have different sizes as well.)
Take a portion of the dough and flatten it with your hands. Add the ready filled plum in the middle and wrap the dough around the fruit. Ensure that you close the seams of the dough well, as otherwise, they might open in the water. Repeat until all the dough is used up.
Leave your raw dumplings to rest on a plate for a further 30 minutes at room temperature.
In the meantime, heat water with ½ teaspoon of salt in a large pot. There should be enough water in the pot to coat the dumplings. Once the water is boiling, reduce the heat, as the dumplings suppose to only “Simmer” not “wildly boil”.
Place the dumplings into the water and leave to simmer for about 10 minutes. You might have to do this in stages depending on the size of your pot.
In a separate frying pan melt the butter. Then add the breadcrumbs and fry until golden brown. Remove from the heat.
Once the dumplings are cooked, remove them with a slotted spoon. Add them to the pan with the breadcrumbs and roll them around until coated.
Serve warm. Before serving sprinkle with cinnamon sugar or serve with vanilla sauce.