Preheat oven to 250°F (120°C) and line a baking sheet with parchment paper.

In a medium saucepan, combine brown sugar, light corn syrup, butter, and salt. Heat over medium, stirring until a rolling boil, about 4–5 minutes.

Once boiling, reduce heat and let simmer for 5 minutes without stirring. Remove from heat and stir in baking soda and vanilla extract.

In a large mixing bowl, pour the freshly popped popcorn and drizzle hot caramel sauce over it. Toss to coat evenly.

Spread caramel-coated popcorn on the prepared baking sheet. Bake for 1 hour, stirring every 15 minutes.

Remove from the oven and let cool completely on the baking sheet. Break apart and serve or store in an airtight container.