01 - Preheat the oven to 350°F.
02 - Combine crushed saltine crackers, melted butter, and granulated sugar in a medium mixing bowl. Stir until the crumbs are evenly coated.
03 - Firmly press the cracker mixture into the bottom and up the sides of a 9-inch pie dish.
04 - Bake the crust for 15 minutes, or until lightly golden. Remove from oven and allow to cool slightly.
05 - In a separate bowl, whisk together the sweetened condensed milk, egg yolks, lemon juice, and lime juice until the mixture is fully blended.
06 - Pour the lemon-lime filling into the pre-baked crust.
07 - Return to the oven and bake for 15 to 18 minutes, until the filling is just set but slightly wobbly in the center.
08 - Let the pie cool at room temperature for 30 minutes, then refrigerate for a minimum of 2 hours.
09 - Before serving, beat the chilled heavy whipping cream with powdered sugar using an electric mixer until soft peaks form.
10 - Spread the whipped cream evenly over the chilled pie. Garnish with lemon or lime zest if desired. Slice and serve cold.