Celeriac, or celery root, is the swollen, knobbly, edible base of Apium graveolens var. rapaceum — a cultivar of wild celery bred not for its stalks but for the dense, ivory-fleshed mass at the crown of the plant. Beneath a rough, gnarled brown skin lies firm, pale flesh that tastes of celery crossed with nutty parsley: clean, savoury, faintly sweet and earthy. A humble, long-keeping winter vegetable, it is grated raw into the classic French céleri rémoulade, puréed and mashed with potato, roasted into wedges, or simmered into soups and stocks.