1. Preheat oven to 250 degrees F (95 degrees C). Place popcorn in a very large bowl.
2. In a medium saucepan over medium heat, melt butter. Stir in caremal, corn syrup and salt. Bring to a boil, stirring constantly. Boil without stirring 4 minutes. Remove from heat and stir in soda and vanilla. Pour in a thin stream over popcorn, stirring to coat.