Preheat oven to 350.
Butter a 9" pie pan.
Process graham cracker crumbs, butter and sugar in food processor until combined.
Press mixture into bottom and sides of prepared pan.
Bake 8 minutes or until set.
Set aside to cool.
Whip egg yolks and lime zest until fluffy.
Slowly add in condensed milk while continuing to beat.
Beat until thick and fully incorporated.
Add lime juice and beat at low speed just until combined.
Pour into crust.
Bake for 10 minutes or until filling sets.
Cool on wire rack.
Refrigerate for several hours.
Freeze for 15 minutes before serving.
Whip cream and sugar until stiff peaks form.
Garnish pie with whipped cream before serving.