Grease and line the base of a solid-bottomed 23cm/9inch round cake tin (a springform is best)
Preheat the oven to 180C/160C fan/Gas 4
In a large food processor pulse the chocolate and sugar until fine. Add the boiling water, butter, egg yolks, coffee powder and vanilla extract.
In a glass bowl, whisk the egg whites until stiff and then fold them into the chocolate mixture
Pour the mixture into the prepared cake tin and bake in the hot oven for about 45 – 55 minutes. The top will be cracked like a desert fault line.
After you take the cake out of the oven it will collapse into itself quite a bit. This is ok – its not meant to be a proud cool cake, its meant to be slightly rough around the edges and the crème fraiche and berries will hid any dips and cracks
Let the cake cool, then put it in the fridge for a few hours. When you are ready to serve, remove from the tin, smother the top in crème fraiche, then raspberries, strawberries and redcurrants (or blueberries, blackcurrants and blackberries). You can also grate some more chocolate on top or dust some icing sugar