Pour 1 tablespoon of oil into a 4-quart saucepan; heat over high heat. Add 1/2 cup of popping corn; keep pan moving constantly until corn stops popping, about 3 to 5 minutes. Remove pan from heat and transfer popped corn into a dish; set aside and keep warm. Repeat until all corn has been popped.

Stir sugar, condensed milk, corn syrup, and butter together in a medium saucepan over medium heat; bring to a boil and simmer until it reaches 240 degrees F (115 degrees C) on a candy thermometer. Stir in vanilla.

Pour caramel over popped corn and stir to coat.

Lightly grease your hands and shape popcorn mixture into 15 balls; let cool completely.