I use celeriac to mimic all my old potato favourites including mash, chips, boiled and roasted. using all purpose seasoning can help to "amend" the strong celery flavour, but personally I like it anyways. I do note however that roast celeriac always seems to resemble parsnip.
My next experiments will be, spinach and celeriac "aloo" (curried potato and spinach) and bombay potatos!.
All the best - Steve