Preheat your oven to 250°F (120°C). Line two large baking sheets with parchment paper or lightly grease a large roasting pan.

Place the popped popcorn in a large bowl and remove any unpopped kernels.

In a medium saucepan over medium heat, melt the butter. Stir in the brown sugar, corn syrup, and salt until combined.

Bring the mixture to a gentle boil. Allow it to boil for 4-5 minutes without stirring.

Remove the saucepan from the heat and carefully stir in the baking soda and vanilla extract. The mixture will foam up slightly.

Immediately pour the caramel sauce over the popcorn and toss until all the popcorn is evenly coated.

Spread the coated popcorn onto the prepared baking sheets or roasting pan.

Bake for 45 minutes, stirring every 15 minutes to ensure even coating and crispness.

Remove from the oven and allow the caramel corn to cool completely.

Break apart any large clusters and serve or store in an airtight container.