In a small saucepan, break the chocolate into pieces, add the butter, sugar, 2 tablespoons of water and melt in a bain-marie.
When everything is well melted and forms a smooth cream, add the egg yolks, stirring well, the preparation still being kept in a bain-marie.
Then remove from the heat to incorporate the stiffly beaten egg whites.
Chill, reserving a spoonful of mousse for decoration.
Line the bottom and sides of a buttered loaf pan with ladyfingers, domed side against the pan.
Then fill the mold by alternating layers of chocolate cream and biscuits dipped one by one for 3 or 4 seconds in the sweetened coffee.
Put in the fridge overnight.
Turn out onto a long dish, spread the cream reserved for decoration on the cake and sprinkle with granulated chocolate
