In a bowl, combine the egg yolks and lime zest. Whisk together for 2-3 minutes until the mixture turns a light green color. Add the sweetened condensed milk and stir until combined. Add lime juice, and stir until combined. Cover with plastic wrap and set aside for 30 minutes at room temp to allow the mixture to thicken. Start working on the crust.

Preheat oven to 325 F.

In a food processor, add the sugar and graham cracker pieces and pulse until there are fine crumbs. Slowly add the melted butter and pulse until just combined and there are no dry crumbs. Press the crumbs into a 9" pie plate. Bake until the crust becomes fragrant and lightly browned, about 13-15 minutes. 

Remove the pie plate from oven and pour filling into the crust. Smooth out the filling with an offset spatula, and return back into the oven for 10-15 minutes or until filling is firm but still jiggles slightly. 

Let the pie cool at room temp for about an hour, then cover with plastic wrap (be careful not to let the plastic wrap touch the pie filling or it will stick). Refrigerate for about three hours or until the filling is set. 

Whip the cold whipping cream either in a stand mixer with whisk attachment or with a hand mixer. When the whisk starts to leave trails in the cream, add the powdered sugar and whip until it is stiff. Smooth over the pie and serve with additional lime zest for garnish, if you'd like. Enjoy!