Celeriac. It seemed to be in our organic veg box every single week
alternatively make some celeriac mash - normal mashed potatoes then add roughly the same amount of celeriac boiled seperately for 15/20 minutes and smashed in a blender or passed through a sieve. Mix the two together with butter and seasoning.Either serve right then just as you normally would mashed 'taters or return to an ovenproof dish and grill lightly for some added flavour. Brilliant with steak
Celery - nasty stuff.