Active time: 40 min. Start to finish: 4 1/2 hrs
6 lbs. (2- to 3-inch pieces) meaty oxtails
1 1/2 tsp. salt
1 tsp. black pepper
1 1/2 tbsp.. extra-virgin olive oil
1/4 lb. Tía Paquita chorizo
1 large onion, coarsely chopped
4 medium carrots, coarsely chopped
4 garlic cloves, chopped
1 Turkish or 1/2 California bay leaf
1/2 tsp. sweet or hot Spanish smoked paprika
1 cup dry white wine
1 (28- to 32-oz.) can whole tomatoes in purée, coarsely chopped (including purée) in a food processor
2 tbsp. chopped fresh cilantro
1 tbsp Sherry vinegar or red-wine vinegar
Special equipment: an 8- to 9-quart heavy pot
Prepare oven to 350°
Pat oxtails dry and sprinkle with salt and pepper. Heat oil in pot over moderately high heat until hot but not smoking, then brown oxtails in batches without crowding, turning occasionally, about 5 minutes per batch. Transfer as browned to a bowl. Pour off all but 1 tbsp. fat from pot.
Remove and discard casing from chorizo, then finely chop sausage in food processor.
Cook chorizo, onion, carrots, garlic, and bay leaf in fat in pot over moderate heat, stirring occasionally, until onion is softened, 6 to 7 minutes, Add paprika and cook, stirring 1 minute. Add wine and bring to a boil, stirring and scraping up and brown bits. Add oxtails with any juices accumulated in bowl and chopped tomatoes (liquid should come about halfway up sides of meat) and bring to a boil.
Cover pot and braise oxtails in lower third of oven, turning once or twice, until very tender, 3 to 3 1/2 hours. Skim fat from sauce, then stir in parsley, cilantro, vinegar, and salt and pepper to taste.
Oxtails improve in flavor if braised 2 days ahead (add parsley, cilantro, and vinegar just before serving). Cool, uncovered, then chill, surface covered with parchment paper or wax paper and pot covered with lid. Remove any solidified fat before reheating.
You can also braise oxtails in a roasting pan. First brown oxtails in a 12-inch heavy skillet, then transfer them to a roasting pan just large enough to hold oxtails in 1 layer.