For the struklji first prepare the dough: Mix buckwheat flour and wheat flour. Knead with 125 ml of lukewarm water, one egg and a pinch of salt to form a smooth dough. Cover and let rest in a cool place for 30 minutes.
For the filling, mix well curd cheese, sour cream, eggs, sugar, vanilla sugar and soft butter.
Flour a work surface and roll out the dough to the thickness of the back of a knife. Cut out circles with a cookie cutter or glass. Place a tablespoon of filling in the center of each piece of dough and brush the edges of the dough with a little water. Fold the dough over the filling and press the edge slightly with fork tines.
Bring plenty of salted water to a boil and let the dumplings steep more than boil, about 10 minutes. Lift out.
Melt butter in a large frying pan. Add powdered sugar and breadcrumbs and stir through. Arrange the struklji on plates and sprinkle the crumbs on top.