Chocolate Mousse

First make the mousse. Construct a bain-marie by filling a large pan one-third full of water. Bring to a simmer In a bowl big enough to fit over the pan without its bottom touching the water, place the chocolate and let it melt gently without stirring. Add the orange zest to the melting chocolate (do not stir the chocolate, or it will seize). When the chocolate has melted, remove from the heat and set aside to cool.

Whisk the double cream in a large bowl using an electric whisk until it starts to thicken. Add the cooled chocolate and whisk for 20 seconds, then use a plastic spatula to fold the mixture together carefully and ensure that the chocolate is entirely integrated with the cream. Refrigerate for a minimum of 2 hours.

To make the ganache, put the chocolate pieces and cocoa powder into a large bowl. Heat the milk and cream over a medium heat until almost boiling and slowly pour over the chocolate, stirring well. Add the brandy and stir until silky smooth. Allow to cool, then cover with clingfilm and refrigerate for at least 2 hours.

To make the crumble, preheat the oven to 160°C/300°F/gas 2. Put the flour, sugar and cocoa into a food processor. Add the butter and pulse gradually until you have a crumble consistency. Take the mixture out of the processor and bring it together with your hands to make a dough. Spread evenly over a non-stick baking tray and bake in the oven for 15 to 20 minutes, or until it has a soft biscuit-like texture. Set aside to cool.

To serve, divide the mousse equally between 8 tumblers or glass dishes. Spoon the ganache over the mousse and sprinkle with the biscuit crumble.