Grease a 20cm cheesecake tin that will fit inside a pressure cooker. Mix biscuit crumbs and cinnamon together. Sprinkle on the base of the tin, pressing gently.
Melt chocolate and butter together and set aside.
With a food processor or table top mixer, beat cream cheese until smooth. Add chocolate mixture and blend until mixture is well-mixed and uniformly coloured. Add cream, vanilla, sugar and eggs. Beat well. Sieve cocoa powder over batter and pulse or mix on low speed until cocoa is thoroughly incorporated. Pour mixture over biscuit base in tin. Cover cake with a piece of baking paper. Cover entire cake tin with tin foil.
Add water to pressure cooker. Place cake tin on the trivet in pressure cooker. Seal cooker. Bring up to high pressure. Reduce heat to stabilise pressure and cook 45 to 50 minutes. Remove cooker from heat and let the pressure drop on its own. Remove cheesecake from cooker and let cool to room temperature in pan on a cooling rack.
Remove cheesecake from tin and chill for 8 hours before serving.