In a bowl with a hand mixer, or bowl of a stand mixer, beat together the softened cream cheese, and sweetened condensed milk until combined and no lumps remain.
** Best way to soften cream cheese is to place the unwrapped cream cheese onto a microwave-safe plate and microwave for 30-45 seconds. You want it soft to prevent lumps in the filling mixture, but not boiling hot. So watch carefully.
Add in the key lime juice and powdered sugar and blend until combined. Pour mixture into the prepared graham cracker crust and smooth out the top.
When ready to serve combine the heavy whipping cream, powdered sugar, and key lime juice into a bowl. Beat together until thick and stiff peaks form. Spread on top of the pie or put inside a piping bag with a tip and pipe it on top of the pie.
You can either mix the lime zest into the whipped cream or zest it on top of the pie as shown in the pictures.
If you prefer to make your own graham cracker crust that's totally fine. Just make sure it's the 9" pie size.
DO NOT get the graham cracker crust that is '2 extra servings'. You just want the 6 oz sized crust.
You will find key lime juice in the juice aisle of the grocery store. It's usually by the lemon juice. If you really can't find it, you can substitute with lime juice but I really recommend getting the key lime.
When zesting the lime only zest on the very outer surface of the skin. The more you zest into the skin, the more bitter the lime zest will become.
If you want more of a strong key lime flavor then do not add the powdered sugar into the filling mixture. Maybe taste it before you add the powdered sugar and see what you think. As the pie sits in the fridge the flavors develop and it does get slightly sweeter.