Pop your popcorn. You can use the oil or air pop method just don't use the pre-packaged microwave kind.
Place in a large mixing bowl. I use my dutch oven because it's wide and deep.
Prepare the baking pan with nonstick spray.
Preheat the oven to 250F.
Prepare the caramel coating
In a medium saucepan combine the butter and brown sugar.
Cook over medium heat until the butter is melted and the brown sugar is dissolving.
Bring to a boil.
Boil for 5 minutes.
Remove from heat and add the vanilla extract and salt.
Stir to combine.
Add the baking soda and stir carefully. THIS WILL CAUSE IT TO FOAM AND BUBBLE so make sure your pot is big enough to handle that.
Quickly drizzle the caramel mixture over your popcorn.
Stir to coat all the popcorn as evenly as possible.
Bake the popcorn to set the caramel
Pour the popcorn onto the prepared baking sheet.
Spread out as evenly as possible.
Bake for 1 hour, stirring every 15 minutes.
Remove from the oven and let cool completely.
Store in an airtight container for up to 1 week.
Notes
For easier clean up, coat your cookie sheet in aluminum foil or parchment paper.
If you need to, make sure to prepare a few large baking sheets so that your popcorn can be spread out evenly.
Use a candy thermometer to monitor the heat of the caramel sauce mixture, so that it doesn’t burn and stays the correct temperature. Continuously stir with a wooden spoon to prevent sticking to the bottom of the medium pot.
If you’re somewhere with a high altitude, reduce the temperature to low heat, adjusting by 2 degrees for every 1000 feet above sea level.
For the stickier, thicker kind of popcorn you can add in a light corn syrup to your caramel sauce mixture.
(Originally Published 06/05/18 - photos and recipe notes updated to improve user experience)