this recipe might be a bit difficult for you on the other side of the pond, as you don't have quark over there..
this recipe asks for Schicktkaese, which is a special form of quark, roughly said, it's a bit more dry, almost crumbly.
A recipe for Quark you find here: homemade-quark-german-quark-14449.html
for the dough:
500g Schichtkaese (or very dry quark)
50g butter, roomtemperature
pinch of salt
for the future I think I would add some sugar to the dough...
plums without stone, about 10 to 15.
ca. 50g ground poppyseeds
ca. 30g confectioner's sugar
cream butter and eggs, then add the Schichtkaese and salt, mix well until you get a smooth dough. Let rest for at least 10min.
now mix cinnamon and sugar as you like and toss the plums in the mixture
with wet hands form Knoedel about the size of a tennisball and try to get a plum inside - for me this is the hardest part
bring salted water to cook, put in the knoedel and let simmer for about 25-20min depending on the size.
Mix the poppyseeds with the sugar and add to the melted butter.
serve the Knoedel warm with the poppy-butter.
Alternatively you may serve it with confectioner's sugar alone.
Sounds a bit complicated, but I hope you'll understand...