Add the onion wedges, potatoes, star anise, cinnamon sticks and lamb shanks. Turn the lamb to coat well in the sauce. Cover the tray tightly with foil and place in the oven.
Bake for 2 hours.
Remove the foil and return the tray to the oven. Bake uncovered for a further 1 to 1½ hours, turning the lamb twice during cooking, until the meat is browned and tender. Skim off any excess fat from the top of the sauce. Spoon the sauce over the lamb shanks so they are well coated.
Serve the lamb with the curry sauce spooned over the top.
Garnish with sliced red chilli and coriander, and serve with steamed jasmine rice.