Grease and line the base of an 8-inch square or 9-inch round cake pan (though I prefer to use a springform pan as the texture of the cake is quite moist and sticky).
Preheat the oven to 350º F.
In a large food processor (or do in two batches), pulse the chocolate and sugar until fine.
Add the boiling water, butter, egg yolks, coffee and vanilla extract.
In a glass bowl, whisk the egg whites until stiff and then add them to the mixture in the food processor and blend for 10 seconds or so.
Pour the mixture into the prepared cake pan and put in the hot oven for 45–55 minutes.
The top will be cracked like a desert fault line.
Let the cake cool, then put it in the fridge for a few hours.
Remove from the pan and smother it in raspberries, strawberries and crème fraîche.
You can also grate some more chocolate on top.
After you take the cake out of the oven it will collapse in on itself quite a bit.
This is OK; it’s not meant to be a proud cool cake, it’s meant to look slightly rough around the edges and homemade, and the crème fraîche and berries will hide any dips and cracks!