1. PLACE the dark chocolate, butter and syrup in a saucepan and melt over a moderately low heat, stirring often, until smooth. Stir in the biscuits and raisins, spoon into a plastic lined 28cm x 18cm slice pan and gently smooth over. Refrigerate until set.
2. POUR the melted milk chocolate over the slice and then refrigerate until firm. Cut into 16 pieces. Store in an airtight container in the refrigerator until required.