Pop 1/2 cup popcorn kernels using an air popper or stovetop method
Remove any unpopped kernels and place the popcorn in a large bowl
Preheat the oven to 250°F
In a saucepan, melt 1/2 cup butter over medium heat
Add 1 cup brown sugar, 1/4 cup corn syrup, and 1/2 teaspoon salt
Stir and bring the mixture to a boil
Boil for 4 to 5 minutes without stirring
Remove from heat and stir in 1/2 teaspoon baking soda and 1 teaspoon vanilla extract
Pour the caramel over the popcorn
Toss until the popcorn is evenly coated
Spread the coated popcorn on a baking sheet lined with parchment paper
Bake for 45 minutes, stirring every 15 minutes
Remove from the oven and let cool completely
Break apart the caramel popcorn and serve