Line a 20cm (base measurement) square cake pan with non-stick baking paper, allowing 2 sides to overhang. Place the ice-cream in a large bowl and set aside for 10 minutes or until softened slightly. Stir in biscuit until combined. Spoon into pan. Smooth the surface. Place in freezer for 30 minutes or until firm. Line a baking tray with non-stick baking paper. Turn the ice-cream mixture onto a chopping board. Place 8 wafers side-by-side, in a single layer, on top of the ice-cream. Use a large sharp knife to cut the ice-cream into slices, using the edges of the wafers as a guide. Turn over each ice-cream stack. Top with remaining wafers. Spread the Peppermint Crisp over a plate. Press the edges of the sandwiches into Peppermint Crisp to coat. Place on the lined tray. Place in the freezer for 1 hour or until firm. Cut in half diagonally and dust with icing sugar to serve.