Also called celeriac, celery knob or turnip-rooted celery, celery root is the root of a celery plant (not the same variety that produces the familiar supermarket celery bunches) grown specifically for its root, although both the leaves and stalks are edible.
The gnarled, knobby brown root bulb may look impenetrable but once the outside is peeled, the tender ivory flesh is delicious either raw (usually shredded in salads) or cooked. Celery root tastes similar to common celery but has a more pronounced nutty, earthy flavor and a softer, denser texture. Boil it as you would a potato, then mash; add it to stews or soups; or chop or shred it raw and add it to salads.
Buy firm, medium-size roots, about the size of small grapefruits, that feel heavy for their size and are free of bruising and soft spots. Tangled root ends are acceptable, as are any green stalks growing from the top. Celery root is available from early fall through early spring.
Trim any greenery and root ends from the celery root and store the unwashed roots in a perforated plastic bag in the vegetable crisper of the refrigerator for 3 to 5 days.
Scrub the celery root with a stiff bristle brush under cold running water. Trim the root further if it appears tough or particularly fibrous and then use a vegetable peeler or small, sharp knife to peel the brown skin. Immediately sprinkle the root with lemon juice to prevent discoloring. For cooking, cut, chop or shred the root using a knife, food processor or shredder.
Adapted from Williams-Sonoma Kitchen Companion (Time-Life Books, 2000).