In a large mixing bowl, using an electric hand whisk on medium-high speed, whisk the cream cheese and sugar until smooth and fluffy.
Add the flour and salt and whisk until combined.
Set the mixer to low speed, add the eggs, one at a time, and whisk just until combined. Do not over-whisk
With the mixer still on low, mix in the sour cream and vanilla extract.
Take 1 cup of the filling and add to a medium bowl. Add the cocoa powder and whisk on low speed till combined.
Pour the white cheesecake filling first into the prepared crust. Then, gently pour the chocolate filling into the middle of the pan. Use a wooden skewer to swirl the two batters together.
Tap the pan gently on a table or kitchen counter a couple of times to get rid of any air bubbles. Cover the pan with aluminum foil
Pour water into the inner pot of the Instant Pot and then put the cheesecake pan on a trivet and lower into the Instant pot
Lock the lid in place and set the valve to SEALING.
Set to HIGH pressure for 35 minutes.
When the timer goes off allow the Instant Pot to do a Allow the pressure to do a natural release for 15 minutes, then flip the valve to VENTING and release the remaining steam.
Open the lid and remove the springform pan from the Instant Pot. Take the aluminum foil off of the cheesecake pan and gently mop up any moisture on the cheesecake surface with a paper towel.
Cool the cheesecake in the springform pan on a wire rack until it reaches room temperature.
Cover the cheesecake, still in the pan, with a plastic wrap and refrigerate for at least 6 hours, or overnight preferably.
When ready take off the plastic wrap and gently remove from the springform pan. Serve as is or decorate with chopped chocolate bunnies and sliced Cadbury crème eggs.