How to Make It
Preheat oven to 250°F. Line a large rimmed baking sheet with parchment paper. Whisk together butter, sugar, and salt in a very large bowl. Add popcorn, and fold gently until popcorn is evenly coated in mixture. Spread in prepared pan.
Bake in preheated oven 30 minutes, stirring every 10 minutes. Remove pan to a wire rack and cool completely. Popcorn can be stored in an airtight container for up to 1 day.