Line a 1kg loaf tin with cling film. Mix together the orange juice and brandy and use to soak the biscuits. Dip the biscuits into the orange mixture and line them along the base and up the long sides of the tin (they will stand above the rim). In a bowl, mix together the ice-cream with the mincemeat. Spoon half of the ice-cream mixture over the base and even out. In another bowl, mix together the cranberries, walnuts, orange zest and crumble in the Amaretti biscuits. Sprinkle half of the mixture over the ice-cream in the tin. Spoon over the remaining mincemeat and ice-cream mixture, then fold over the sponge fingers above the rim and press down lightly. Fill the gap down the middle with 2 more soaked sponge fingers. Press down lightly into the filling, cover with the excess cling film and freeze for at least 2 hours. To serve, turn out onto a plate, remover the cling film and spoon over the melted chocolate, making sure it dribbles down the sides. Quickly sprinkle over the remaining Amaretti and nut mixture as the chocolate will freeze and set immediately. Dust with the icing sugar and serve immediately.