Put the chopped chocolate, cocoa powder, water and brandy in a heat-proof bowl. Place over a saucepan of 2.5cm barely simmering water. Stir frequently, until all ingredients are blended and smooth. Remove from heat.
Mix in 100g of the sugar, a little at a time, until smooth. Add the chocolate mixture to the tofu and puree until smooth and well blended. Spoon the mousse into serving dishes, cover and refrigerate for at least 1 hour.
Whip the cream until it is almost completely whipped, add the remaining half a teaspoon of sugar and finish whipping. Top each serving with a dollop of whipped cream and a sprinkle of chocolate.