Place the digestives in a bag and smash up with rolling pin until they look like breadcrumbs.
Add the melted butter to a saucepan and stir in the biscuit mixture
In a greased lose base tin press the biscuit mixture down firmly to evenly cover the base. Put into the fridge whilst you prepare the cheesecake mixture
Melt the chocolate and put to one side to cool slightly.
Beat ¾ of the cream into the mascarpone and cream cheese, and then stir the chocolate and orange liqueur into the cream cheese mixture
Spoon the filling onto the biscuit base and leave to set for at least 2 hours
Zest the oranges and mix the zest into the remaining cream.
Serve the cheese cake with a little dollop of orange cream and a couple of segments of the orange.