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 tiramisu emulsion: Mix the coffee, cognac, double cream and icing sugar together in a bowl and whisk until you get soft peaks.
To finish the dessert, remove the glasses from the fridge 5 minutes before serving. Top the mousse with the crumble and finish with the tiramisu emulsion and a dusting of cocoa powder.
«Vary the flavour of the mousse by adding a liqueur to the cream, amaretto would work very well.»