Sieve the wheat flour and rye flour into a bowl. Make a well in the center, add the sourdough, and cover it with a little flour. Let rise in a warm place for about 1 hour until roughly doubled in size.
Add the quark, some milk, and salt to the bowl. Mix all ingredients together to form a firm dough. Beat the dough with a wooden spoon for 8-10 minutes until bubbles form and the dough separates from the sides of the bowl. Cover and let rise in a warm place for about 1.5 hours.
Turn the dough onto a floured work surface and roll it out. Cut into oval or round pieces. Cover the pieces and let them rise for 15-20 minutes.
Heat the clarified butter or oil in a large skillet over medium-high heat. Fry the pieces until golden brown on both sides, about 3-4 minutes per side.