Graham Cracker Crust:
1 1/2 cups crushed graham crackers (about 9 to 12 crackers, at least one sleeve)
5–6 tablespoons butter, melted
Optional Ingredients:
1 teaspoon cinnamon
1/4 cup sugar
Filling:
4 egg yolks (reserve 2 egg whites)
1 can (14 ounces) sweetened condensed milk
1/2 cup fresh-squeezed lime juice (about 20 key limes or 6 Persian limes)
2 teaspoons fresh lime zest (optional but zesty!)
Topping:
1 cup heavy whipping cream
3 tablespoons sugar
Prepare the Graham Cracker Crust: To crush crackers, place in a ziplock plastic bag, push out all the air, and roll over them with a rolling pin. in a bowl—or directly in the pie dish to avoid washing more dishes—mix melted butter into cracker crumbs. If you like, mix in cinnamon and/or sugar. Press mixture into pie plate with your fingers or with the bottom of a glass. Bake at 350°F for 10 minutes.
Prepare the filling: Whisk 4 egg yolks in a large bowl, and then add condensed milk, lime juice and lime zest.
Beat 2 reserved egg whites until stiff, and fold into mixture. This will make your filling lighter. (This is an optional step, but one that I always do.) Pour filling into prepared crust.
Bake at 350°F for 20 minutes or until filling is set. Let cool, and then chill for at least 3 hours. (Waiting is the hardest part!)
Prepare the topping: Beat cream and sugar until peaks form. Spread over top of pie. Alternatively, use your leftover egg whites to make a meringue topping. I prefer the whipped cream over the meringue for its sense of freshness.