Stir the melted butter into the crushed biscuits, mixing well. Press into a 20.5 cm (8 inch) spring-clip tin. Chill. Beat together the cheese and sugar until smooth. Stir in most of the cream, reserving a little for decoration. dissolve the gelatine by sprinkling over the orange juice in a small bowl and standing over a pan of hot water. Fold into the cheese mixture. Beat in the melted chocolate and pour over the biscuit base. Chill until set. Remove cheesecake from tin and place on a serving dish. Pipe or spoon reserved cream on top and decorate with mandarin orange segments. drizzle with a little melted chocolate.