Spread popped popcorn in a thin layer onto tinfoil and set aside. Heat sugar in a heavy bottomed pan over a medium heat, stirring constantly with a metal butter knife (it cleans easier). The sugar will start to form gooey clumps, but keep stirring. Once the sugar has melted and turned a deep caramel colour, remove it from the heat and work the last clumps of sugar around until dissolved. Pour caramel over the popcorn in a thin, steady stream. Use the stirring knife to work the caramelised popcorn around with one hand while sprinkling liberal amounts of Maldon salt over the popcorn with the other. Once the popcorn is sufficiently coated and salted, leave it to cool (until the caramel is brittle) and then place in a serving bowl.