Pour popped popcorn into a large roasting pan and set aside.
In a medium-sized saucepan, melt the butter.
Add the packed sugar, corn syrup, salt and mix well.
Bring the mixture to a boil.
Reduce the heat and allow to cook for 5 minutes without stirring.
Preheat the oven to 250F
Remove the pan from the heat and stir in the vanilla extract and the baking soda.
Pour the caramel mixture over the popcorn and stir well to evenly coat the popcorn with the caramel sauce.
Cover the pan with aluminum foil.
Bake for 1 hour, making sure to stir every 10 minutes.
Remove from the oven and allow to cool completely.
When cooled, shake the pan to break up the caramel corn.
Serve and enjoy or store in an airtight container.