Chill the graham cracker crust while you make the filling.
Evenly pour the filling into a chilled 9-inch graham cracker crust.
Using a handheld mixer or stand mixer, beat the heavy whipping cream to stiff peaks. Transfer to a separate bowl.
In the same bowl (no need to wipe out), beat cream cheese for a couple minutes until creamy. Stream in the sweetened condensed milk and mix until smooth. Add the key lime juice and mix until combined.
Gently fold the whipped cream into the cream cheese mixture. (Fold, do not stir or whisk.)
Cover with plastic wrap and refrigerate overnight (or at least 6 hours.)
Garnish, slice, and serve.
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Notes
If you want to make a homemade graham cracker crust, it's easy: In a bowl, combine 1 1/2 cups fine graham cracker crumbs, 1/3 cup granulated sugar, and 6 tablespoons melted unsalted butter. Press the mixture into the bottom and sides of a 9-inch pie dish. Chill for 30 minutes. Proceed with the recipe as written.