Line the bottom of a 9-inch springform pan with about 18 ladyfinger halves; set aside.
Combine the chocolate, 1/3 cup sugar, water, and a few grains salt in the top of a double boiler; heat over boiling water, stirring until smooth.
Stir about 3 tablespoons of the chocolate mixture into egg yolks.
Immediately blend into mixture in double boiler top and cook over boiling water, stirring constantly, about 5 minutes.
Remove from water and set aside to cool.
Stir in the rum.
Cream the butter with the extract; add the confectioners' sugar, a small amount at a time, beating until light and fluffy after each addition.
Blend in the chocolate mixture; set aside.
Beat egg whites until frothy; gradually add the remaining V3 cup sugar, beating constantly until stiff peaks are formed.
Fold whipped cream into chocolate mixture, then spread meringue over chocolate mixture; fold together.
Fold in the macaroon crumbs.
Pour one half of the mixture into the spring-form pan over the layer of ladyfingers.
Arrange 18 ladyfinger halves over the chocolate mixture and cover with remaining one half of mixture.
Chill until firm, 12 hours or overnight.
Remove ring from springform pan and set cake on serving plate.
Press remaining ladyfinger halves onto sides of mold.
Garnish with unsweetened whipped cream and coarsely shredded unsweetened chocolate.