Add the popcorn to a very large bowl or paper bag, set aside.
6 quarts plain popped popcorn
Preheat the oven to 250 degrees F. Spray two 9×13 baking dishes with cooking spray, set aside.
Add the brown sugar, butter, corn syrup, and salt to a dutch oven or large stockpot.
2 cups light brown sugar, 1 cup salted butter, ½ cup dark corn syrup, 1 ½ teaspoons fine sea salt
Place over medium heat, and stir constantly until the butter is melted and the sugar dissolves.
Stirring occasionally, bring the mixture up to a boil (about 10 minutes). Once at a boil, boil for 5 minutes carefully stir occasionally.
After 5 minutes take off the heat. Immediately stir in the vanilla and baking soda.
1 ½ tablespoons vanilla extract, ¾ teaspoon baking soda
Pour half of the caramel over the popcorn. If using a bowl, stir to combine. If using a paper bag (I find this easier), close the top of the bag and shake vigorously.
Add the rest of the caramel over the popcorn, stir or shake again until it is as evenly coated as you can get it.
Divide the popcorn among the two baking dishes.
Place in the oven and bake for 45 minutes, stirring every 15 minutes.
Lay out a large sheet of parchment or wax paper over the countertop.
Spread out the caramel corn and try to break up any clumps. Allow to cool completely and enjoy.
Notes
Use fresh popcorn: Make sure your popcorn is freshly popped and free of any un-popped kernels for the best results.
Don’t skip the baking soda: The baking soda is key to getting that perfect, crispy texture, so don’t leave it out.
Work quickly: When adding the caramel mixture to the popcorn, work quickly to ensure that the popcorn gets evenly coated.
Bake it low and slow: Baking at a low temperature for a longer time helps it stay crisp and allows the caramel to set perfectly.
Stir often: Stirring during baking helps it cook evenly and prevents it from sticking together in clumps.
Cool completely: Let it cool completely on parchment paper before storing it to keep it from sticking together.