8full graham crackersprocessed to fine crumbs (1 cup)
5tablespoonsunsalted buttermelted and warm
4teaspoonsgrated zest plus 1/2 cup strained juice from 3 to 4 key limes
4large egg yolks
1 14-ouncecan sweetened condensed milk
Whipped Cream Topping
1/2key limesliced paper thin and dipped in sugar (optional)
For the crust
Adjust oven rack to center position and heat oven to 325° F. In a food processor, pulverize graham crackers until evenly fine. Add sugar and pulse a couple times until combined. Continue to pulse while adding warm, melted butter in a steady stream; pulse until the mixture resembles wet sand. Transfer the crumbs to a 9-inch pie plate and evenly press the crumbs into the pie plate. Bake the crust until it is fragrant and beginning to brown, 15 to 18 minutes. Transfer to a wire rack and cool completely.
For the filling
Whisk zest and yolks in medium bowl until tinted light green, about 2 minutes. Beat in milk, then juice; set aside at room temperature to thicken, about 30 minutes.
Pour lime filling into crust and bake until center is set, yet wiggly when jiggled, 15 to 17 minutes. Return pie to wire rack and cool to room temperature. Refrigerate until well chilled, at least three hours.
For the whipped cream
Up to 2 hours before serving, whip cream in medium bowl to very soft peaks. Adding confectioners’ sugar 1 tablespoon at a time. Continue whipping to until stiff peaks form. Decoratively pipe whipped cream over filling or spread evenly with rubber spatula. Garnish with optional sugared lime slices and serve.
Pie can be covered with lightly oiled or oil-sprayed plastic wrap laid directly on filling and refrigerated up to one day.