- Arrange oven racks in top and bottom thirds of oven. Preheat oven to 300F. Line two baking sheets with parchment. Place popcorn in a large wide bowl.
- Stir sugar with 1/2 cup water and salt in a large heavy-bottomed saucepan set over medium. Stir until sugar dissolves, about 2 to 3 min. Increase heat to high. Bring to a boil, without stirring, until mixture turns amber, 5 to 7 min. Remove from heat and stir in butter and nuts. Very carefully pour hot mixture over popcorn. Immediately stir to mix using a heatproof spatula or wooden spoon.
- Spread popcorn mixture in one layer over prepared baking sheets. Bake for 10 min, then stir and switch sheets. Continue baking until popcorn is crunchy, 10 more min. Remove and let cool completely. Popcorn will keep well, stored in an airtight container, for up to 5 days.
- Prep Tip: Have all your ingredients ready before cooking caramel.