Mix graham cracker crumbs, sugar, and melted butter until evenly moistened.
Press the crumb mixture firmly into the base and sides of a 9-inch pie plate to form a crust.
Preheat oven to 350°F (175°C).
In a stand mixer with whisk attachment, beat egg yolks and lime zest on high speed until light and fluffy, about 5 minutes.
Gradually add sweetened condensed milk while continuing to beat for 3 to 4 minutes.
Reduce speed and slowly add fresh key lime juice, mixing until smooth and combined.
Pour filling into prepared crust and smooth the surface evenly.
Bake for 10 minutes until just set.
Remove from oven and cool to room temperature, then refrigerate until thoroughly chilled.
Chill a metal mixing bowl and whisk in the freezer for 10 minutes.
Add heavy whipping cream and sugar to chilled bowl and whisk until stiff peaks form, taking care not to over-whip.
Top the chilled pie with freshly whipped cream before serving.