Use a melon baller or teaspoon to carefully remove the cores of the pears through the bases, then level the bottoms so they sit flat. Put the pears into a pan with the sugar, 100ml of the sherry, the star anise, cinnamon stick and 400ml of water. Heat slowly over a low heat, then simmer gently with a lid on for 15-20 minutes or until the pears are very tender (this may take longer, depending on how ripe the pears are). Use a slotted spoon to remove each onto a plate. Keep the poaching syrup for adding to cocktails, if you like.