This is something I have recently tried and it worked really well and tasted really good, so I thought I would share it with you gals/guys.
1 cup butter
2 cups brown sugar
1/2 cup corn syrup
1 teaspoon salt
1/2 teaspoon baking soda
1 teaspoon vanilla extract
5 quarts popped popcorn
DIRECTIONS:
Preheat oven to 250 degrees F. Place popcorn in a very large bowl.
In a medium saucepan over medium heat, melt butter. Stir in brown sugar, 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.
Place in two large shallow baking dishes and bake in preheated oven, stirring every 15 minutes, for 1 hour. Remove from oven and let cool completely before breaking into pieces.