Put the tea bags, cloves, cardamom, cinnamon, vanilla pod, lemon zest and 400ml/14fl oz cold water in a deep, medium saucepan and bring to the boil. Reduce the heat, add the sugar and heat gently until dissolved. Add the pears so they are sitting snugly. They should be covered with liquid so add more water if necessary. Cover with a lid and cook over a very low heat until they are soft, about 15-20 minutes depending on their size.
Transfer the pears to a serving dish and cover to keep warm. Return the pan to the hob over a high heat and boil the syrup vigorously until syrupy, about 20 minutes.You should be left with about 200ml/7fl oz. Pour over the pears and serve with crème fraîche, if using.