Combine the chocolate, 1/2 cup sugar, and water in the top of a double boiler over boiling water.
Cook and stir until mixture is smooth.
Stir about 3 tablespoons hot mixture into well-beaten egg yolks.
Return to mixture in a double-boiler top.
Cook and stir over boiling water about 5 minutes.
Remove from heat and set aside to cool slightly.
Stir in the extract.
Cream the butter with the confectioners' sugar until light and creamy.
Beat in the chocolate mixture until thoroughly blended.
Set aside.
Line the sides and bottom of a 9-inch spring-form pan with the ladyfingers; set aside.
Beat the egg whites until frothy; gradually add the 6 tablespoons sugar, beating constantly until stiff peaks are formed.
Fold into the cooled chocolate mixture until evenly blended.
Spoon into ladyfinger-lined pan.
Chill at least 24 hours.