"Preheat the oven to 450°F. In a large roasting pan combine the oxtails, patted dry and seasoned with salt and pepper, the onions, and the carrots. Roast mixture in the middle of the oven, turning the oxtails as they are browned, then transfer all of it to a large stockpot. Deglaze the roasting pan with the wine over high heat, scraping up the brown bits, and add the deglazing liquid to the stockpot with the water, celery root, garlic, thyme, bay leaf, and peppercorns. Bring the liquid to a boil, skimming the froth, and simmer gently, uncovered, for 4 hours.Ladle the mixture through a sieve lined with a rinsed and squeezed kitchen towel into a large bowl. Reserve the oxtails for another use, such as oxtail pate, or simply eat them. Discard the remaining solids. The stock can be made 3 days in advance and kept chilled. Discard excess fat (leave enough to cover soup when chilled). "