Preheat the oven to 350°F. In a small bowl, Mix the graham cracker crumbs with the melted butter.
Press the crumbs into the bottom of a 7-inch springform pan and up the sides about 1/2 an inch.
Bake until fragrant and set, 5 to 6 minutes. Let cool.
Beat the cream cheese in a medium bowl with a hand mixer until very smooth.
Add the sugar and beat until well blended.
Add 2 tablespoons of sour cream, the heavy cream, the vanilla, and the lemon zest and beat to combine.
Add the eggs, one at a time, and beat until incorporated.
Pour the cheesecake mixture into the prepared crust.
Gently smooth the top. Place a piece of aluminum foil over the top, and be sure to crimp it over the sides of the pan.
Pour 1 cup of water into the Instant Pot. Place a trivet with handles in the pot and place the pan on top. If your trivet doesn’t have handles, use a foil sling to make removing the pan easier.
Lock the lid into place. Select Manual function and adjust the pressure to High. Set cooking time to 25 minutes.
After cooking, naturally release the pressure for 10 minutes, then quick release any remaining pressure.
Carefully remove the cheesecake from the pot and remove the foil. The cheesecake should be set, with the center slightly softer than the edges.
Mix the remaining 2/3 cup of sour cream and the sugar in a small bowl.
Spread this mixture over the hot cheesecake.
Let the cheesecake rest at room temperature for 15 to 20 minutes, then refrigerate until thoroughly chilled, 3 to 4 hours.