Preheat the oven to 300 degrees. Line a large rimmed baking sheet with parchment paper.
Pour the popped popcorn into a large serving bowl; set aside. In a small saucepan melt together the butter, brown sugar, corn syrup and 1 teaspoon of the salt over medium heat. Bring the mixture to a boil. Boil for 4 minutes without stirring.
Pour the caramel mixture over the popcorn and toss the popcorn to coat it evenly. Pour the popcorn into the lined pan, sprinkle the remaining salt on top (1/2 to 1 teaspoon, depending on your personal taste preference) and place the pan in the oven. Bake for 30 minutes, stirring every 10 minutes.
Allow the popcorn to cool on a parchment paper-lined counter.