Beat the chestnut puree to lighten it. Whip the cream (not stiffly); fold in cinnamon, chestnut puree and chocolate. Divide among 4 heat-proof ramekins and smooth level. Chill 1 hour. Preheat the grill to highest setting. Sprinkle sugar on evenly; grill until bubbling. Leave to cool but serve within 2 hours to prevent the sugar softening. The sugar can of course be caramelised using a salamander or culinary-torch
Cooked, shelled chestnuts are blended to a smooth puree. You can make your own or purchase at online at Amazon.com.