What to do with the rest?
Puree is the most basic recipe: Alton Brown makes a straight-up celeriac puree that is ... pretty much just celeriac. Gourmet adds apples. EatingWell makes it with parsnips and potatoes.
Soup is a common use: Tiny Urban Kitchen has a tasty-looking celeriac-apple-potato soup recipe. FatFree Vegan Kitchen makes a (fat-free vegan) creamy celeriac soup.
NPR calls celeriac "the unsung frog prince of winter vegetables" and suggests a recipe for french-fried celeriac. Less charitably, Gordon Ramsay notes -- with his soup, dauphinoise, and curry recipes -- that "If there was a competition for the world’s ugliest vegetable, celeriac would take first place every time."
(I'm not actually sure what a dauphinoise is, but you can bet I'll be researching it -- and the pronunciation -- for our next go-round in the kitchen. Gourmet does a gratin with potato and Stilton, which I suspect is pretty much the same thing as a dauphinoise.)
What are you making with yours?