This is a family favorite that my mom has been making my whole life.
1/4 c. butter
1/2 c. corn syrup
1/2 t. vanilla
1 c. brown sugar
2/3 c. sweetened condensed milk
3/4 c. popcorn, popped
In saucepan, combine butter, sugar and corn syrup. Stir well and bring to a boil over medium heat. Stir in sweetened condensed milk; simmer, stirring constantly for 5 minutes. Stir in vanilla. Pour over popcorn and stir to coat.