Combine finely crushed graham crackers, ⅛ tsp salt, and brown sugar.
Melt the 4 tablespoon of butter and mix in the graham mixture.
Line bottom and sides of 7" springform pan with parchment paper.
Press graham cracker crust into the bottom of the pan and use the back of a spoon to gently press it up on the sides.
Bake the crust in the oven for 15 minutes.
Meanwhile, using a food processor, combine the room temperature cream cheese, and heavy cream. Blend using short pulses.
Add in the sugar, cornstarch, 2 tsp vanilla, salt, lime juice, and key lime zest. Quick Pulses until just incorporated. Scrape down sides of bowl as necessary.
Add in the room temperature eggs and blend using short pulses until just combined. This part is critical!
Pour into the parchment paper-lined springform pan and allow the filling to settle.
Gently pick up the springform pan and "tap" it onto the counter to pop any air pockets that may be in the filling. Smooth out the top with a spatula.
Loosely cover the top of the pan with aluminum foil.
Pour 1 cup of water into the pot and put the trivet into place.
Create a sling out of foil or use an Instant Pot silicone sling and place it in the Instant Pot.
Gently place the cheesecake in the Instant Pot and close the lid.
Set the pot to MANUAL and cook for 42 minutes.
Allow the Instant Pot to Natural Release for 18 minutes before removing the lid.
Carefully remove the cheesecake from the Instant Pot and carefully remove the foil (careful not to drop any liquid on the cake.). Use a paper towel to soak up any water that may be laying on the cake.
Allow the cheesecake to sit on the counter for 10 minutes before moving the cheesecake to chill in the refrigerator for 24 hours.
Once cheesecake is chilled, it is safe to remove the cheesecake from the pan.
Homemade Whipped Cream
Stir together 4 tablespoon of water and 1 teaspoon of unflavored gelatin and heat in microwave for 5 seconds. It will dissolve. Allow it to cool before adding to the heavy cream, otherwise, it will melt.
In a larger bowl, combine 1 cup of heavy cream and beat until small peaks form.
Add in 4 tablespoon of confectioner's sugar and 1 tsp of vanilla. Beat.
Add in the cooled gelatin and beat until still peaks form.