Leave the peel on the pears and cut them in half, down through the stems to the base. Scoop out the core, then put in a roasting tin with the cut sides up. Spoon the sherry into the core cavity of each pear and the water into the base of the tin. Sprinkle the spices over the pears, including the cardamom pods and their black seeds. Dot with the butter, then sprinkle with the sugar.
Remove the rind from the orange and sprinkle into the tin. Cut the orange into wedges and squeeze the juice over the pears. Add the wedges to the base of the roasting tin.
Cook in a preheated oven, 180°C (350°F), Gas Mark 4, for 25 minutes until tender and just beginning to brown, spooning the pan juices over the pears halfway through cooking and again at the end.
Spoon into shallow dishes, drizzle with the pan juices and serve with crème fraîche or Greek yogurt.