Preheat oven to 140°C or 120°C fan-forced. Pour boiling water halfway up the sides of a deep baking dish and place dish at bottom of oven. Lightly spray a 19cm-round springform tin with oil. Line base with baking paper. Place biscuits in a food processor and process to form crumbs. Combine crumbs and melted canola spread, then press into base of prepared tin.
Place cream cheese, sugar and cocoa powder in food processor and process until smooth. Add eggs and sour cream, processing until smooth. Pour mixture over prepared base, then bake for 35–40 minutes. The cheesecake will still have a definite wobble in the centre. Turn off oven and leave cake to cool inside with door slightly ajar for 1 hour. Place on a wire rack to cool completely before covering and placing in the refrigerator to chill overnight.
To make white chocolate curls, spread white chocolate on a clean work surface to a 10cm-diameter circle. Allow to set for 15–20 minutes, then run an ice-cream scoop across the surface to form curls. Top cake with chocolate curls and serve.