Begin by crushing the digestive biscuits until fine crumbs form. In a mixing bowl, combine the crushed biscuits with melted butter and cocoa powder, stirring until evenly moistened. Press this mixture firmly into the base of a springform tin to create a compact crust. Place the tin in the refrigerator to chill for 30 minutes.

In a large mixing bowl, whisk together cream cheese, icing sugar, and cocoa powder until the mixture is smooth and free of lumps. Gradually pour in double cream, continuing to whisk until the filling thickens and becomes airy.

Once the base is chilled, carefully spoon the creamy filling over it, smoothing the top with a spatula. Cover the cheesecake with plastic wrap and refrigerate for a minimum of 4 hours, preferably overnight.

For the dark chocolate ganache, heat dark chocolate with double cream in the microwave, stirring until fully melted and glossy. Pour this ganache over the top of the chilled cheesecake.

In a small bowl, combine white chocolate with double cream and heat gently until melted. If desired, mix in Sugarflair superwhite powder. Allow this ganache to cool slightly before piping the spiderweb design atop the set dark chocolate ganache.

Using a piping bag, carefully pipe a spiral of the white chocolate ganache over the dark ganache. Then, use a cocktail stick to draw lines from the center outward to shape the web design.

Once everything is set, remove the cheesecake from the springform tin. Using a warm knife, slice the cheesecake into portions and serve chilled, paired with fresh berries or chocolate sauce.