Combine the crushed biscuits with the melted butter and mix really well to coat. Press the mixture into a clingfilm lined 23 cm (9 inch) tart or cake tin and chill in the freezer or refrigerator while you are making the filling.
Beat the cream cheese or mascarpone cheese with the chocolate spread, orange rind and caster sugar until thick and smooth. Spoon over the biscuit base and smooth down evenly. Return to the freezer or refrigerator for at least 20 minutes or until required, then remove and decorate with grated orange-flavoured chocolate to serve.