Preheat The Oven & Prep Your Pans. Preheat oven to 250 degrees and lightly grease a rimmed baking sheet with spray oil or a little butter.
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 a very large bowl, discarding any unpopped kernels. (If you have extra popcorn, keep it close by in case you want to add it in later.)
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.)
Boil The Caramel Sauce 5 Minutes. Watch the clock and boil the caramel sauce 5 minutes, stirring constantly.
Remove From Heat & Finish. After 5 minutes, quickly remove the caramel sauce from the heat and whisk in vanilla, cinnamon, and baking soda. (This will make the caramel sauce bubble and foam.)
Quickly Pour Caramel Over The Popcorn. Pour the caramel sauce mixture over the popcorn and stir to coat. I recommend pouring about half of the caramel sauce over the popcorn, then stirring and adding the pecans and the rest of the caramel sauce to any "dry" spots as needed. This makes it a bit easier to coat it evenly. Stir until the popcorn and pecans are pretty evenly coated. 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.)
Spread The Popcorn Out On Your Prepared Pan. Transfer the cinnamon caramel popcorn mixture to the prepared baking sheet and spread out fairly evenly. (Don't worry about a few clumps here and there!)
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 60 minutes total.
Spread The Caramel Corn Out Onto Parchment Paper or a FRESH parchment lined baking sheet to cool completely to room temperature. Do NOT leave the popcorn on the original baking sheet or it will stick! Wait until the caramel corn is completely cool before drizzling with white chocolate.
Drizzle With Chocolate. Add white chocolate melts to a small microwave safe bowl. Microwave on low power in 15-20 second intervals, stirring in between each interval until the white chocolate is melted and glossy. Drizzle over the cooled caramel pecan popcorn and let the white chocolate set.
Cool, Serve & Store. Let the white chocolate set completely, then break the popcorn into clusters and transfer to an airtight container or bags.