Preheat the oven to 180°C. Select a roasting dish or ovenproof dish that will hold the shanks nicely.
Lay lamb in the dish in one layer and scatter in potatoes and onion.
Mix the curry paste with coconut milk and stock and pour over meat and vegetables. Add the star anise, cinnamon sticks and chilli flakes. Turn the lamb to coat in sauce, then cover tightly with two layers of foil or a lid.
Bake for 1½ hours then remove the foil or lid (careful of the steam) and bake for a further 30 minutes, turning the lamb a few times to brown evenly. The meat ought to be super tender and the sauce thickened.
Serve with rice or naan and garnished with fresh coriander.