Combine the flour, sourdough powder, quark and water, cover and leave to rest for approx. 12 hrs. at room temperature.
Using the dough hook on a hand mixer, knead the flour, salt, water, yeast and starter dough on the lowest setting until a soft dough is formed. Add a little water or flour as required, cover and leave to rest for approx. 3 hrs. at room temperature. Knead the dough once more, shape into a round, brush with a little water, sprinkle with poppy seeds, cover and leave to rise for approx. 1 hr.
Approx. 1 hr. in the centre of an oven preheated to 200°C. Remove from the oven, allow to cool a little, then leave to cool completely on a rack.