How to Make It
Preheat the oven to 325°F. In a large enameled cast-iron Dutch oven or heavy pot, heat the olive oil. Season the oxtails with salt and pepper, and add half of them to the pot. Cook over moderately high heat until the oxtails are browned all over, 4 to 6 minutes. Transfer to a plate and brown the remaining oxtails.
Add the sweet potatoes to the pot and cook over moderate heat, stirring occasionally, until the potatoes just begin to soften and brown, about 5 minutes. Add the jalapeño and cook, stirring occasionally, until softened, about 2 minutes. Add the wine and scrape up any browned bits from the bottom of the pot. Bring to a boil, and cook until the wine is reduced by half, about 5 minutes. Add the veal stock, 2 cups water, oranges, herb sprigs, cinnamon, and bay leaves, and bring to a simmer. Return the oxtails to the pot; cover and transfer to the oven. Braise until the meat is very tender, about 3 hours.
Discard the oranges, herb sprigs, cinnamon, and bay leaves. Skim off and discard any fat, and season with salt and pepper before serving.