Preheat the oven to 180'C.
Bring 320ml double cream to the boil in a saucepan. Break the chocolate into small pieces if necessary and place in a heatproof bowl.
When the cream comes to the boil, pour the cream onto the chocolate and stir until all of the chocolate has melted and you have a glossy ganache. Allow the ganache to cool slightly for around 5 minutes.
In another bowl, lightly whisk the remaining 430ml double cream until it just begins to thicken.
Fold this cream into the ganache until evenly distributed.
Transfer the mixture to a piping bag and pipe the mixture into 6 glasses. Refrigerate for at least 30 minutes to allow the mousse to set.
Whilst the chocolate cream is setting, make the crumble: Scrape the seeds from the vanilla pod. Rub the butter, sugar, vanilla, ground almonds and flour between your fingertips to make a crumble. Spread on a baking tray and bake for 15 to 20 minutes. Allow to cool and break the crumble up with your fingers.
For the coffe emulsion: Mix the coffee, double cream and icing sugar together in a bowl.
Pour the mixture into a syphon. Screw on the lid tightly and shake the syphon. Charge it with the compressed gas and refrigerate until ready to serve.
To finish the dessert, remove the glasses from the fridge 5 minutes before serving. Top the mousse with the crumble and finish with the coffee emulsion and a dusting of cocoa powder.
«Vary the flavour of the mousse by adding some orange zest to the chocolate ganache mix.»