Slice enough pound cake to get 18 (1/3") slices. Line sides and bottom of an ungreased 9" springform pan with 12 to 14 slices of pound cake. Set remaining pound cake aside. Dissolve espresso in 3/4 cup boiling water; stir in 1/4 cup Kahlúa. Brush pound cake with 3/4 cup espresso mixture, setting aside remaining 1/4 cup espresso mixture.
Whisk together 6 egg whites and 3/4 cup sugar in top of a double boiler; place over simmering water, and cook, whisking often, until mixture reaches 160°. Transfer egg white mixture to a large bowl; beat at high speed with an electric mixer until stiff peaks form. Set aside.
Sprinkle gelatin over 1/2 cup cold water in a saucepan; let soften 1 minute. Cook over medium heat, stirring until gelatin dissolves. Add 1/4 cup whipping cream; set aside.
Whisk together 6 egg yolks, remaining 1/2 cup sugar, and remaining 1/4 cup Kahlúa in top of double boiler. Place over simmering water, and cook, whisking often, until mixture reaches 160°. Remove bowl, and beat at medium speed with a handheld electric mixer until thick and pale. Add mascarpone cheese and gelatin mixture, beating until smooth. Fold in about 1 cup meringue; fold in remaining meringue. Spoon half of mascarpone mixture into springform pan. Top with remaining pound cake slices; brush pound cake slices with remaining 1/4 cup espresso mixture.
Place half of chocolate morsels in a glass bowl. Microwave on HIGH 1 1/2 minutes; stir until smooth and slightly cool. Add 1/2 cup mascarpone mixture, stirring until smooth; fold into remaining mascarpone mixture. Spoon chocolate mascarpone mixture into springform pan. Chill 20 minutes or until slightly firm on top.
Combine remaining chocolate morsels, remaining 1/4 cup whipping cream, and butter in a small glass bowl. Microwave on HIGH 1 1/2 minutes. Stir until chocolate melts and mixture is smooth. Spoon chocolate ganache over top of dessert, spreading to edges with a small offset spatula. Cover and chill at least 8 hours.
Before serving, run a knife around edge of pan to release sides. Remove Charlotte to a serving plate; let stand 20 minutes. Garnish, if desired.
*Substitute 12 ounces cream cheese if you can't find mascarpone cheese.