Mix together the graham cracker crumbs, sugar and melted butter in a bowl until well combined.
Press the mixture into the bottom of your small spring-form pan. Set aside.
For the cheesecake filling:
In a large mixing bowl with a hand mixer, or in the bowl of your stand mixer fitted with the paddle attachment, add the cream cheese and sugar and mix well to combine on medium speed.
Mix in the cornstarch, lemon zest, lemon juice, vanilla and salt, one at a time, mixing after each addition.
Add the sour cream and mix well to combine, scraping down the sides of the bowl.
Add the egg, and then the egg yolks one at a time, mixing after each addition and scraping down the sides of the bowl to make sure everything is incorporated.
Pour the cheesecake filling into the prepared pan over the graham cracker crust and smooth out the top.
Cover the pan tightly with 2 layers of aluminum foil. You can even add a sheet of kitchen paper towel under the aluminum foil (take care that the foil or paper doesn't rest on the top of the cheesecake filling) to absorb excess liquid and prevent condensation.
Add 1 1/2 cups water to the bottom of your Instant Pot. Place the pan on the trivet and lower the trivet into the Instant Pot.
Add the lid to the Instant Pot and set the valve to sealing.
Set the Instant Pot to pressure cook on high pressure for 22 minutes. Once the 22 minutes of cooking have passed, let the Instant Pot naturally release pressure for 15 minutes.
Immediately remove the pan from the Instant Pot and remove the foil covering.
For the topping:
Mix together the sour cream, lemon juice and sugar in a bowl until creamy and smooth.
Spread the mixture over the hot cheesecake right after you remove it from the Instant Pot. Spread the mixture evenly and in a thin layer.
Let the cheesecake cool to room temperature, and then place it in the fridge to chill for about 4-6 hours or overnight. This will ensure clean slices.
Serve the cheesecake with your favourite berry sauce or some fresh fruit.
Video
Notes
This cheesecake is best enjoyed the day after it's baked. Store it in the fridge uncovered for the initial chilling time (to prevent a soggy top due to condensation), and then store any leftovers in the fridge in an airtight container.