The best celery root is available in the fall and through the winter. At farmers’ markets, in CSA boxes, and at natural foods stores, these roughly round taproots with tough, yellowish white or grayish brown skin look like gnarly, hairy, muddy-bottomed orbs, better left alone than embraced for their culinary possibilities. Don’t pass them up. They keep well and are brilliant mashed, raw in salads, turned into a silky soup, or braised in a stew. Buy celery roots that feel heavy for their size and are firm with no soft spots. Overly large specimens are often spongy at the center, and very small ones offer little flesh once the tough outer skin is pared away. Look for softball-size roots, weighing 1 to 1½ pounds/455 to 680 grams.