Preheat oven to 350°F.
Stir together crushed crackers, melted butter, sugar, and egg white in a medium bowl until combined.
Transfer mixture to a 9-inch glass pie plate; firmly press on bottom and sides. Freeze 10 minutes.
Bake in preheated oven until crust is lightly browned, about 20 minutes. Transfer to a wire rack; cool slightly, about 10 minutes.
Meanwhile, whisk together condensed milk and egg yolks until smooth. Whisk in lime juice and lemon juice until combined. Pour lime mixture into warm crust.
Bake at 350°F until center is just set, about 15 minutes. Transfer to a wire rack; cool 1 hour. Refrigerate until chilled, about 2 hours.
Beat cream and powdered sugar in a large bowl with an electric mixer on high speed until stiff peaks form, about 2 minutes.
Spread whipped cream topping over chilled pie, leaving about a ½-inch border of custard showing around crust. Garnish with lemon and lime zests, if desired.
