1. Line the inside edge of a 9-inch springform pan with split ladyfingers standing on end, like making a round fence. Sprinkle them with liqueur.
2. In the top of a double boiler, blend the gelatin and sugar.
3. To the contents of the double boiler, add the milk and egg yolks. Using a rotary beater, blend the mixture thoroughly. Over simmering water, cook the custard, stirring constantly, until it coats a metal spoon. Transfer it at once to a large mixture bowl.
4. Stir in the orange rind, juice, and orange juice concentrate (thawed). Chill mixture until it just begins to set, perhaps an hour. If you wait too long, it won't mix properly.
5. Fold in the whipped cream. Pour the mixture into the springform pan, taking care that the ladyfingers remain upright. Chill the Charlotte Russe for at least 6 hours, or until thoroughly set. Umold the dessert onto a chilled serving plate and offer it in wedges (as you would cut a cake). The Charlotte Russe may be embellished with candied orange zest, if desired.