Line a 9×9-inch brownie tin with parchment paper, leaving the edges hanging over the sides; set aside. Place the lightly crushed cornflakes in a large bowl; set aside.
In a medium sized bowl, whisk together the butter, chocolate, and golden syrup. Pour over the cornflakes and stir together until everything is evenly coated.
Transfer the cornflake mixture to the prepared brownie tin & use an offset spatula to squish it firmly down and into the corners – we want it to be sturdy.
Evenly spread the cornflake crunch mixture over the top of the cornflake layer, lightly pressing down so it adheres to the chocolate.
Next, the chocolate layer. Pour the melted chocolate over the top of the cake & use an offset spatula to spread it evenly around, trying not to disturb the cornflake crunch layer beneath.
Sprinkle the reserved cornflake crunch across the top of the chocolate layer.
Place in the fridge for at least two hours before lifting out of the brownie tin & slicing into 16 squares. Transfer the squares to the freezer & eat from frozen.