Grease or coat with non-stick spray, a 15cm (7-inch) springform cake tin. To further prevent the cheesecake from sticking I suggest adding a parchment round to the bottom.
Add the digestive biscuits (or Graham crackers) to a bowl and finely crumb (by hand or electric mixer). Add the cinnamon. Melt the butter and add to the crumbs. Mix until combined.
Add the crumb mixture to the cake tin and press down well. Place the tin in the freezer whilst you prepare the filling.
Using a hand mixer, blend together the cream cheese, sugar, double (heavy) cream, cornflour, lemon juice & zest and vanilla extract. Scrape the bowl as needed. Mix well for around 2 minutes.
Add the eggs one at a time and beat in gently. Do not over blend.
Remove the cake tin from the freezer and add the filling. Tap the cake tin to remove air bubbles. Loosely cover with tin foil.
Place the trivet in the instant pot and add 300ml (1.5 cups) of cold water.
Make a sling using tin foil and use it to lower the cake tin into the instant pot.
Put the lid on and set to high pressure for 30 minutes. Allow to naturally release (around 20 minutes).
Remove the cake tin from the instant pot and place on a cooling rack. Remove the foil.
Whisk together the sour cream, vanilla extract and icing (powdered) sugar. Add to the hot cheesecake.
Leave on the cooling rack for around an hour and then place in the fridge for a further 24 hours whilst the cheesecake develops its flavour.