II
The Method
1
Pat the oxtail segments thoroughly dry. Heat the olive oil in a large heavy-based casserole over high heat. Brown the oxtail in uncrowded batches, turning each piece to develop a deep mahogany crust on all sides. Remove each batch and set aside. The Maillard crust formed here is the flavour foundation of the dish; crowding the pan causes steaming and must be avoided. The crust is done when it releases cleanly from the base and is uniformly dark golden-brown.
2
Reduce the heat to medium. In the fat remaining in the casserole, cook the soffritto — celery, carrot, and onion — stirring frequently until completely softened and beginning to turn golden. Add the white wine and allow it to reduce by half, scraping up any caramelised residue from the base. The wine is spent when its sharp raw alcohol smell has left the casserole.
3
Return all browned oxtail to the casserole. Add the crushed tomatoes and enough water to bring the liquid level to just below the top of the meat. Season with salt. Cover tightly and transfer to an oven set at 160 °C, or keep at the lowest possible stovetop heat, for a minimum of 3.5 hours. This is where the dish lives or dies: collagen in the oxtail must convert fully to gelatin — no shortcut in time is possible. The braise is ready when the meat yields completely to a gentle probe and the exposed bone pulls free without resistance.
4
Lift the oxtail segments from the casserole and set aside. If the braising liquid appears watery, return the casserole to high heat uncovered and reduce until the sauce coats the back of a spoon with a visible glossy film.
5
Add the blanched celery hearts, pine nuts, drained sultanas, and candied citron peel (if using) to the sauce. Sift in the unsweetened bitter cocoa powder and stir to incorporate fully. Return the oxtail to the casserole. Simmer uncovered for 30 minutes. The finished sauce should be glossy, complex on the nose — bitter, sweet, and savoury at once — and cling to the oxtail when a piece is lifted.
6
Taste the sauce for salt and the balance of bitter, sweet, and sour. The cocoa should register as depth rather than dominance; the sultanas and citron should provide a clean sweet-sour lift against the gelatinous richness. Rest the dish, covered, for at least 15 minutes before serving — or refrigerate overnight and reheat gently, which allows gelatin and all flavour elements to fully integrate.