Brush a 19 x 29cm (base measurement) lamington pan with melted butter to lightly grease. Line the base and sides with non-stick baking paper, allowing it to overhang slightly.
Combine the butter, condensed milk and golden syrup in a medium saucepan over low heat. Cook, stirring, for 5 minutes or until butter melts and mixture is smooth. Transfer to a large heatproof bowl. Add the biscuits, coconut and licorice allsorts and stir until just combined. Press the mixture into the base of the prepared pan and set aside for 30 minutes to set.
Place the chocolate and copha in a heatproof bowl over a saucepan half-filled with simmering water (make sure the bowl doesn't touch the water). Use a metal spoon to stir over low heat until chocolate melts and mixture is smooth. Pour the chocolate mixture over the slice in the pan. Place in the fridge for 1 hour to set. Cut into squares to serve.