8 cups plain popped popcorn (don't use butter or kettle corn varieties; plain microwave popcorn is fine)
1 cup packed brown sugar
1/3 cup water
1/3 cup light corn syrup
1/4 cup butter
1/2 teaspoon salt
1 teaspoon good vanilla extract
Place popcorn in a large mixing bowl and set aside. In a heavy saucepan, combine brown sugar, water, corn syrup, butter and salt. Bring to a boil over medium heat, stirring constantly. Continue cooking (but no stirring) until 270 degrees is reached on a candy thermometer (soft crack stage).
Promptly remove from heat; stir in vanilla. Pour over mixture over popcorn, taking care to stir until evenly coated. Quickly shape into 8 balls once mixture is cool enough to handle.