Filling
4 teaspoons grated lime zest
1/2 cup lime juice from 3 to 4 limes (or use bottled Key Lime Juice)
4 large egg yolks
1 (14-ounce) can sweetened condensed milk

Graham Cracker Crust
11 graham crackers , chopped into fine crumbs (1 1/4 cups)
3 tablespoons granulated sugar
5 tablespoons unsalted butter , melted

Whipped Cream Topping
3/4 cup heavy cream
1/4 cup confectioners’ sugar

To prepare the Filling: Whisk together the lime zest and yolks in a medium bowl for about 2 minutes. Beat in milk, then lime juice; set aside at room temperature and let thicken.

To prepare the crust: Place oven rack in the center position and preheat oven to 325 degrees F. Mix graham cracker crumbs and sugar in medium bowl. Add butter; combine with fork until well blended. Press mixture into 9-inch pie pan to form an even crust. Bake until lightly browned, about 15 minutes. Transfer pan to wire rack; cool to room temperature, about 20 minutes.

Once cooled, pour lime filling into crust; bake until center is set, about 15 minutes. Return pie to wire rack; cool to room temperature. Refrigerate at least 3 hours.

Prepare the Whipped Cream: Whip the cream in a medium bowl to very soft peaks. Adding confectioners’ sugar 1 tablespoon at a time, continue whipping until peaks are just-stiff. Spread evenly over the filling with a rubber spatula. Serve immediately.