Separate eggs, whip egg whites and cream separately until stiff.
Melt the butter and chocolate carefully in a double boiler.
Beat the egg yolks in a large bowl with 2 tablespoons of hot water until creamy, stir in the sugar until the mixture is light and creamy. Fold in the melted chocolate, then immediately fold in the egg whites and cream (not with the electric mixer!).
Chill in the refrigerator for at least 2 hours. But don`t serve too cold.