Preheat your oven to 250°F (120°C).
Line a baking sheet with parchment paper.
Over medium heat melt the butter in a large saucepan.
Add the brown sugar, corn syrup, and salt to the saucepan and stir until everything is combined.
Bring the mixture to a boil while increasing the heat to high and stirring constantly.
Once the mixture reaches a boil, let it boil for 5 minutes without stirring.
Remove the saucepan from the heat and stir in the baking soda and vanilla extract until everything is combined.
Pour the caramel mixture over the popped popcorn and stir until all the popcorn is coated.
On the prepared baking sheet spread the popcorn out evenly.
For 1 hour bake the popcorn in the preheated oven, stirring every 15 minutes.
Now it's time to remove the popcorn from the oven and let it cool before serving.