Photograph: Tara Fisher
Pour 1.5 litres of cold water into a medium pan. Split the vanilla pod in half lengthways and scrape out the seeds. Add the pod and seeds to the water with the sugar and bring to a simmer, stirring occasionally to dissolve the sugar. Add the pears and place a piece of baking paper on top to keep them submerged, then simmer gently for 20 minutes.
Insert a skewer or small sharp knife into the pears to test whether they're tender. If not, simmer for a further 5 minutes. When the pears are cooked, leave them to cool in the syrup for at least a couple of hours, preferably overnight, to give them time to take on the flavour of the vanilla.
To make the sauce, put the chocolate in a bowl. In a pan, bring the cream to the boil with the crushed cardamom seeds, then pour it over the chocolate. Leave to stand for a couple of minutes until the chocolate has melted, then stir the sauce gently until smooth. Do not over mix or the sauce may split – the cocoa solids will separate from the cocoa butter.
To serve, remove the pears from the syrup and stand them upright on individual plates. Pour a generous helping of chocolate sauce over them and serve with a scoop of vanilla ice cream, if you like.
Get ahead: you can prepare the pears up to 2 days in advance and store in the syrup in an airtight container in the fridge. Make the sauce up to a few hours ahead and reheat gently in a bowl over a pan of barely simmering water.
Kitchen secret: keep the leftover sugar syrup in the fridge to use as a base for fruit salads or cocktails.