That, my friends, is a celariac. And it was one of the vegetables found in or CSA box this week. It's also known as celery root. Apparently, its flavor is a cross between celery and a parsnip.
Unlike the romanesco broccoli, I have tried celariac once before, but I've yet to make something with it. My sister, Becky, made me celariac and potato soup once and it was so delicious....so I might get that recipe from her or I might try this celeriac apple potato soup recipe. I also got potatoes and onions in my CSA and I still have a few apples from the orchard.
If you know of any good recipes that use celariac, send them my way! Thanks!
Update: I made the celeriac apple potato soup last night and it was awesome! Dave had three big bowls and he gave it 5 out of 5 jalapenos -- and he usually doesn't like soup for dinner.
And now that we've tasted it raw, I'll tell you that celeriac has the flavor of celery, but a consistency close to a carrot. It'd probably be yummy on a vegetable platter with dip.