Brown the flour with the sweet drippings, add onion, then cover the spider and let the onion steam for a little while; do this over a low heat so there will be no danger of the union getting too brown; add vinegar and soup stock and the sugar. Let this boil until the sauce is of the right consistency. Serve with spaetzlen, using water in place of the milk to form the dough. Pour the sauce over the spaetzlen before serving. By adding more sugar the sauce may be made sweet sour.