For the dumplings: drain quark and squeeze if necessary. Combine with eggs, flour, semolina, white bread crumbs, sour cream, sugar and lemon zest. Knead to a smooth dough. If dough is too wet, add extra flour.
Refrigerate for about 1 hour. With a tablespoon, shape about 8 dumplings. Cook dumplings in lightly salted and boiling water for about 10 minutes.
Remove with a slotted spoon and drain well. Melt butter in a pan and cook breadcrumbs until golden yellow. Combine butter with cinnamon sugar, roll dumplings in the crumbs. Place dumplings into a serving plate and serve immediately.