1. Preheat The Oven & Prep Your Pans. If you’re making crispy caramel popcorn (which we recommend!), preheat the oven to 250 degrees and lightly grease a cookie sheet with spray oil or a little butter.
2. Start By Popping Your Popcorn. If you haven’t already, pop the popcorn before you begin. Measure 12 cups (3 quarts) of popped popcorn and place in your largest mixing bowl, discarding any unpopped kernels. (If you have extra popcorn, keep it close by in case you want to add it in later.)
3. Then Start The Caramel Sauce. In a medium saucepan, combine butter, brown sugar, corn syrup, and salt. Melt over medium heat, stirring regularly until the caramel comes to a boil. (Try not to rush this by cranking the heat up, as dissolving the sugar completely gives you the best texture.)
4. Boil The Caramel Sauce 5 Minutes. Watch the clock and boil the caramel sauce 5 minutes, stirring constantly.
5. Remove From Heat & Finish. After 5 minutes, quickly remove the caramel sauce from the heat and whisk in vanilla and baking soda. (This will make the caramel sauce bubble and foam.)
6. Quickly Pour Caramel Over The Popcorn. Pour the caramel sauce over the popcorn and stir to coat. I recommend pouring about half of the caramel sauce over the popcorn, then stirring and adding the rest of the sauce to any “dry” spots as needed. This makes it a bit easier to coat it evenly. Stir until the caramel is pretty evenly coated. Feel free to stir in some extra popcorn, as desired. Note: the popcorn will not look full-coverage/completely covered in caramel at this point. (There will still be some white spots visible at this point. This will resolve in the oven.)
7. Spread The Popcorn Out On Your Prepared Pan. Transfer the caramel corn to the greased cookie sheet and spread out fairly evenly. (Don’t worry about a few clumps here and there!) If desired, sprinkle with a few flakes of flaky sea salt for a salted caramel effect.
8. Bake The Popcorn. Place the pan of popcorn in the oven and set a timer for 15 minutes. At the 15 minute mark, remove the popcorn from the oven and stir. (The caramel will be more melty and fluid, so the pieces will get more evenly coated with caramel). Return to the oven and bake 15 minute more. Repeat this process two more times, until you’ve baked the caramel popcorn for at total of 60 minutes. 
9. Spread The Caramel Corn Out Onto Parchment Or Waxed Paper to cool completely. Wait until the caramel corn is completely cool before transferring to an airtight container or bags. 

Baked caramel corn will keep in an airtight container about 1 month.