3/4 cup (1 and a half sticks) butter
1 cups brown sugar
1/2 cup corn syrup
1 teaspoon salt
1 teaspoon chili powder, to taste
1/2 teaspoon baking soda
1 teaspoon vanilla extract
2 teaspoons coarse sea salt
5 quarts popped popcorn
Preheat oven to 250F degrees. Place popcorn in a very large bowl.
In a medium saucepan over medium heat, melt butter. Stir in brown sugar, corn syrup, salt and chili powder. 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 sprinkle with sea salt. Let cool completely before breaking into chunks.