Pre-heat your oven to 180°C/Gas Mark 4/ Position. upper middle shelf.
Melt the chocolate and diced unsalted butter in a bowl over a pan of barely simmering water, or on low in the microwave. Stir from time to time.
While the chocolate melts, make the chestnut mixture. Get a small food processor. Add the chestnut puree and cocoa powder. Blend for about a minute until it's completely smooth. Add the cream and blend for 30 seconds or so until it is totally incorporated. Add the egg yolks. Pulse until they are combined.
Whisk the egg whites to firm peaks and slowly add the sugar, whisking the whites until they are firm and glossy.
Mix the beaten egg whites together with the chestnut mixture.
Add a third of this mixture to the chocolate. Stir in quickly so that it doesn’t set. Briskly fold in the remaining egg white mixture.
Line the 6 ouef sur plat moulds first with soft butter, then with Demerara sugar.
Spoon 2 tbsp of caramel sauce into the centre of each. Distribute the chocolate mixture over the top. Flatten it slightly.
Bake for 7 minutes, the top and outsides should be just set and the centre soft and molten. It should wobble a little as you take it out.
Scoop the ice cream into the centres then spoon the brandy over the top. If you’re feeling festive, sprinkle the dried cranberries, orange zest and mint leaves over the top. Finish with a little dusting of icing sugar.