Begin preparing your key lime pie filling. Separate the egg yolks from the whites. Place your egg yolks and white granulated sugar in a bowl and either using a stand mixer or a hand mixer, mix them on medium speed until the yolks look light and fluffy.
Next, slowly add in all of your sweetened condensed milk while continuing to mix. Add in the heavy cream and then the key lime juice while mixing. Finally, add in the key lime zest and mix until all the ingredients are well incorporated.
Remove your pie crust from the freezer and pour your key lime pie filling into the crust.
Next, add 1 cup to 1 1/2 cups of water to your Instant Pot, depending on what size you own, and place the trivet inside the Instant Pot. Place the key lime pie on top of the trivet inside the Instant Pot and cover with aluminum foil.
Close the Instant Pot lid and cook on high pressure for 15 minutes. Allow it to natural release for 10 minutes before engaging the quick release button.
Once the pin drops, you’ll know that all pressure has been released from your Instant Pot. Open the lid and carefully remove your key lime pie from the Instant Pot. If you have a sling, you can easily remove the key lime pie, but if you don’t use oven mitts to handle the trivet carefully so you can remove the pie.
Next, allow the pie to cool down on the counter for 45 minutes to an hour before refrigerating. Refrigerate for 4 hours.
Finally, top off with whipped cream and extra key lime zest if desired and enjoy!