Soften the gelatin sheets in cold water.
Line a charlotte mold with ladyfingers.
Chop the chocolate chop and melt with the butter over simmering water. Remove from heat and let cool.
In a saucepan, warm the milk and crème fraîche slightly.
Squeeze the gelatin sheets well and dissolve in the warm chocolate, stirring until smooth.
Separate the eggs and beat the yolks in a bowl over simmering water until frothy. Stir in the milk mixture and the chocolate.
Beat the egg whites with a pinch of salt to stiff peaks and gradually sprinkle in the sugar. Continue beating to make a glossy meringue that holds stiff peaks. Fold the egg whites into the cooled chocolate mixture and fill lined charlotte mold with the chocolate cream. Add ladyfingers to cover, press lightly, and chill for 5 hours in the refrigerator.
Invert the charlotte onto a serving plate. To serve, garnish with chocolate flakes.