1. Place popcorn in a large bowl. Combine brown sugar, cinnamon, and salt in a small bowl.
2. Drizzle popcorn with butter; toss to coat. Coat popcorn generously with cooking spray. Sprinkle with sugar mixture; toss well.
Kids Can Help: While the popcorn pops, kids can measure the cinnamon-sugar mixture and then toss it with the popcorn and butter.