Preheat the oven to 180 ° C. Line a mold with parchment paper.
Knead the flour with butter, quark, salt and baking powder vigorously with your hands to form a smooth dough. Roll out the dough with a rolling pin between baking paper, place it in the mold and pull up the edge a little.
Cut the leek into rings and fry in hot oil in a small pan, stirring frequently. Season with salt, pepper and paprika and season to taste. Spread on the dough base.
Mix the sour cream with the egg in a small bowl with a fork until smooth and spread on the leek. Then sprinkle the grated cheese on top. Bake for about 30 minutes.
Mix in soured milk, herbs as you like and possibly a little mustard, season with salt and pepper and serve with the leek cake.