Combine macaroons and rum in a shallow dish. Set aside.
Combine chocolate, water, and 1/4 cup plus 2 tablespoons sugar in top of a double boiler. Cook over boiling water until chocolate melts.
Beat egg yolks until thick and lemon colored. Gradually stir one-fourth of hot chocolate mixture into egg yolks; add to remaining hot chocolate mixture, stirring constantly. Remove from heat; cool to room temperature.
Beat egg whites (at room temperature) until foamy. Add remaining sugar, beating until stiff peaks form. Gently fold into chocolate mixture.
Line the bottom and sides of a 9-inch Springform pan with ladyfingers. Spoon half the chocolate mixture into pan. Place macaroon mixture over chocolate mixture. Add remaining chocolate mixture; top with ladyfingers. Cover; refrigerate overnight.
Remove sides of pan; place charlotte on a serving platter. Top with whipped cream, and sprinkle with grated chocolate.