Add 1 Tbls of oil to a 4-qt covered saucepan and heat over high heat. When oil is hot, add 1/2 cup of popping corn. Keep pan moving constantly. When corn stops popping, remove from heat. Place popped corn in the oven to keep warm. Repeat until all corn has been popped. Set aside.

In a medium saucepan with a candy thermometer inserted, combine butter, brown sugar and corn syrup. Stir well and bring to a boiling over medium heat. Stir in condensed milk; simmer, stirring constantly, until thermometer reads 238 degrees F. Stir in vanilla.

Pour caramel over popcorn and stir to coat. Butter hands slightly; shape into balls about 3 1/2 inches in diameter. Wrap in plastic wrap.