Toast the hazelnuts in a large non-stick frying pan on a high heat for 2 minutes, until lightly golden, tossing regularly, then tip into a pestle and mortar, returning the pan to the heat.
Pour in the pears (juice and all), let them get hot, then add the Armagnac. Stand back and carefully set light to the liquor with a match. Let it flame, then leave to bubble and reduce to a lovely syrup.
Meanwhile, crush the hazelnuts and divide between four plates, making a pile on each one.
Spoon the pears on to the plates, cup side up.
Remove the syrup from the heat, then snap most of the chocolate into the pan.
While it melts, top each hazelnut pile with a nice round scoop of ice cream, and shave over the last bit of chocolate.
Mix up the chocolate syrup, drizzle into the pear cups, and serve.