Layer the popcorn on a large baking sheet covered with parchment paper, and set aside.
In a medium saucepan, melt the butter.
Add in the brown sugar, corn syrup, and salt.
Heat over medium heat, to boiling. Boil 4-5 minutes.
Remove from the heat and carefully add the vanilla extract. Stir.
Add the baking soda, and stir again. Caramel should be light and frothy.
Allow the caramel to cool just slightly, and pour over the popcorn.
Carefully toss the popcorn with a plastic spoon or spatula, to coat the popcorn with the caramel.
Allow the popcorn to set and cool completely.
Enjoy!