Line a baking sheet with parchment paper and set it next to the stove.
In a medium saucepan, melt the butter over medium heat then add the brown sugar, honey and salt and stir to combine with a rubber spatula.
Add a candy thermometer to the saucepan and allow the caramel to boil for around 5 minutes over medium heat, to 280 degrees F. If the stove is too hot, the caramel could burn before reaching the correct temperature. Add the crushed popcorn, stir to combine with the rubber spatula then cook for another minute, until the thermometer reaches 300 degrees F., which is the hard crack stage.
Pour the brittle immediately onto the parchment lined baking sheet and press down on the brittle with the rubber spatula until it is flat. Careful because the brittle is hot! Sprinkle the brittle with sea salt.
Set the brittle aside for 30 minutes to harden then break it up with your hands and eat! Store any extra brittle in an airtight container at room temperature.