1.Preheat oven to 180°C.
2.Pack oxtail tightly, in a single layer, in the base of a large flameproof casserole dish. Whisk sauce, stock, sherry, rind, juice, garlic, sugar and pepper in a medium jug until combined; add star anise. Pour mixture over oxtail. Bring to the boil. Cover dish, transfer to oven; cook, covered, for 3½ hours or until oxtail is tender.
3.Discard star anise. Remove oxtail; cover to keep warm. Skim fat from surface of liquid. Add buk choy to dish; simmer, uncovered, on stove top for 5 minutes or until wilted. Return oxtail to dish; cook, uncovered, over high heat, until oxtail is heated through. Season.
4.Serve oxtail with buk choy and cooking liquid, sprinkled with chilli and green onion.
Serve with steamed rice. This recipe is not suitable to freeze.Note