Combine graham, butter, and powdered sugar in mixer until well mixed, then press into a 9-inch pie plate. (Optional: Bake at 350 for 6-8 minutes, just until you can begin to smell the crust baking.) Freeze crust until needed.
Grate the zest from one full lime. Squeeze the juice from fresh limes to make 1/3 cup (approximately 1 1/2 limes) of juice.
Whisk together sugar, yolks, zest, and lime juice in a double boiler and heat until they form a custard. Remove from heat and allow to cool.
Whip egg whites to stiff peaks and then beat in sugar.
Fold egg whites into custard.
Whip cream and confectioner's sugar together to stiff peaks. Fold into custard mixture.
Gently spread the custard mixture into the pie crust and freeze until firm, at least 2 hours.