Line bottom and sides of a 9- inch Springform pan with ladyfingers; reserve remaining ladyfingers. Set aside.
Combine chocolate morsels, 1/4 cup sugar, and water in top of a double boiler. Place over boiling water and cook, stirring constantly, until chocolate melts and sugar dissolves. Remove from heat, and stir in vanilla. Let cool to room temperature.
Beat egg yolks in a large mixing bowl until thick and lemon colored; gradually add chocolate mixture, beating constantly, until thickened.
Beat egg whites (at room temperature) until foamy. Gradually add remaining sugar, 1 tablespoon at a time, beating until stiff peaks form. Gently fold egg whites into chocolate mixture.
Alternate layers of chocolate mixture and ladyfingers in prepared Springform pan, beginning and ending with chocolate mixture. Cover and refrigerate overnight.
Remove sides of Springform pan; place charlotte on a serving platter. Sprinkle generously with powdered sugar; garnish with chocolate curls, if desired. Slice to serve.