Pour 1 litre (1¾pt) water into a large saucepan with a fitted lid. Add the sugar, cardamom and cinnamon stick.
Stir in the vanilla pod and seeds, then bring the mixture to the boil. Reduce to a simmer and add the pears. Cover and cook for 20-25 minutes, then remove the pears and set aside.
Turn the heat back up and boil the poaching liquid for 20 minutes, until reduced and syrupy. Discard the spices.
Serve the pears in bowls with the syrup poured over them and a spoonful of mascarpone or crème fraîche.