Preheat the oven to 180°C.
Grease and line the base of a 23cm springform tin.
Blend chocolate and sugar in a food processor until fine.
Add boiling water, butter, egg yolks, coffee, and vanilla, then blend until combined.
Whisk egg whites in a clean bowl until stiff peaks form.
Gently fold the egg whites into the chocolate mixture using a metal spoon.
Pour mixture into the tin and bake for 45 to 55 minutes.
Cool the cake in the tin and refrigerate for 2 to 3 hours.
Top with crème fraîche, berries, grated chocolate, and icing sugar before serving.