Pour the wine into a deep, non-reactive saucepan. Add the stars anise, cloves, vanilla pod, cinnamon and sugar.
Crack open the cardamom pods with a heavy weight, such as a pestle or rolling pin, then drop them into the wine and bring it to a simmer.
Peel the pears, keeping them whole, their stems attached to hold them by. Lower them into the saucepan, then adjust the heat so the liquid continues at a light simmer.
Let the pears cook until they are just tender, checking their progress regularly with the point of a knife. The cooking time can be anything from 15-50 minutes depending on the ripeness of your fruit.
Remove the pan from the heat. Scoop them gently from the cooking liquor with a large spoon, then set them aside in a bowl or shallow plate.
Place the pan over a high heat and bring the cooking liquor to a bubble, then continue cooking until it has reduced to less than 500ml. Taste the syrup for sweetness, adding a little more sugar if you wish.
Break the chocolate into small pieces and leave to melt in a bowl over a pan of simmering water. Finely chop the pistachios. Halve the pears lengthways and place them in shallow dishes.
Pour over the red wine syrup and scatter with pistachios. Decant the chocolate into a small jug and pour a little over each pear at the table.