Graham cracker crust:Preheat oven to 375.Mix graham cracker crumbs, sugar, and butter in a small bowl.Press the crumb mixture into an 8×9 1/2 inch pie pan.Bake for 7 minutes.Cool for at least 30 minutes.
Key Lime Filling:Preheat oven to 350.Whisk together sweetened condensed milk, sour cream, lime juice, and lime zest in a medium bowl.Pour into prepared graham cracker crust and bake for 10 minutes.Let pie cool slightly before chilling.Chill for at least 3 hours.
Whipped Cream TOpping:Beat heavy cream and sugar together in a mixer until stiff peaks form.Beat in vanilla.Spread or pipe the whipped cream on top of the cooled pie.Top with additional lime zest if desired.
