Step 1

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.

Step 2

Bake in preheated oven until crust is lightly browned, about 20 minutes. Transfer to a wire rack; cool slightly, about 10 minutes.

Step 3

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.

Step 4

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.

Step 5

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. Pie can be stored, covered, without whipped cream topping, in the refrigerator up to 4 days. Spread with topping just before serving.