Preheat oven to 150°C. Grease a 20cm (base measurement) springform pan and line the base and side with baking paper.
Heat a non-stick frying pan over medium heat. Cook the hot cross buns, cut-side down, in 4 batches, for 2 mins or until lightly toasted. Arrange the bun tops, cross-side out, around the side of the prepared pan, pressing to secure. Line the base of the pan with the bun bases, trimming to fit.
Use an electric mixer to beat the cream cheese and sugar in a bowl until smooth. Add the flour, vanilla, orange rind and orange juice and beat until combined. Add the eggs and beat until smooth. Add the sour cream and beat until just combined. Pour over the bun bases in the prepared pan.
Place the pan on a baking tray. Bake for 1 hour or until the filling is just set. Turn oven off. Leave the cheesecake in oven, with the door ajar, for 2 hours to cool. Place in the fridge for 3 hours or overnight to chill.
Transfer the cheesecake to a serving platter. Top with the cream, combined chocolate and chocolate topping.