From my Romanian collection of Sour Soups. In some parts of Transylvania,sour soups are being seasoned with vinegar,everyone adds to its bowl. I omit the vinegar from the recipe,but try it if you want see what's it like. I usually make it with chicken thights,but any parts that can go in it,except breast. Here leftover parts from the chicken are sold specially for soups: wings,backs,necks,sometimes heads and feet(remove after boiling). If celery root is not available,the stalks will do just fine. That's what I do,anyway. When I don't have time for dicing,I just throw everything in the food processor and grate them.