Brush flat surfaces of ladyfingers with liqueur and line sides of a 9-inch springform pan. Line bottom with remaining ladyfingers, overlapping if necessary. Melt semi-sweet chocolate in the top of a double boiler. In separate container, dissolve instant coffee in boiling water. Set aside. Beat egg yolks at high speed until foamy, then beat the sugar in gradually, beating until thick. Reduce speed and add vanilla, coffee, and melted chocolate. In large bowl, beat egg whites until stiff peaks are formed. Stir 1 cup of egg whites into chocolate mixture, then fold in remaining whites. Whip heavy cream and fold into chocolate mixture. Pour into springform pan. Freeze until firm (4-6 hours). Garnish with chocolate curls before serving.