Here is a link to you recent duplicate post of this in case you couldn't find it. Already has some answers on it. ;)

Zeedman's thread on this likely got lost with many others in the recent server problems.

Dave

Here is a link that might be useful: Your first post of this

I grow celeriac every year. Like celery disguised as a (hideously ugly) parsnip. It makes the most delicious creamy soup and puree, as well as roasting really well. In my temperate climate (probably around zone 9) it grows through the winter, which makes a nice change from all the chard and brassicas!
It doesn't have celery's drama-queen attitude: its main requirement is plenty of time in which to grow gnarled and warty with surprising pristine white flesh. You MUST peel them!
Don't let them get too big, 4-5 inches across is good: any bigger and you risk them going 'polystyrene-y' in the middle