I remember asking my gran a few years back why they call it włoszczyzna (Włoszech= Italy, thus my confusion)...
celery root here either so i'll just have to use the celery stocks
they're actually getting quite readily available here (California), though I think it's still safe to say the greatest congregations of EU people are still on the east coast
Some people use onions to make rosół, my grandma used to, but first she used to cut it in a half and blacken it over a flame.
We still do it that way, minus the 'cut in half' part. Just peel the outer layer and cut the roots off, scorch it to a nice black on the outside and toss it in. Sometimes I tie string around it to keep it from falling apart once cooked, but that's optional. It DOES give rosół extra flavor ^_^ yummy.