Knead smooth elastic dough long while and carefully. Prepare the filling: grind the onion in a blender and stir all the ingredients until smooth. Make semicircular crescent-shaped posikunchiki (similar in shape to big varenyky): the seam on the side should be pinched heavily but carefully, so as not to break the shell integrity. The thickness of each posikunchiki should be about 3 mm. Fry on refined oil under a very low heat, choosing its intensity so that the patties brown but the filling does not get too hot. Serve posikunchiki with a sauce of beef stock with vinegar, finely chopped onions and black ground pepper.