
Preheat the oven to 250℉. Line two large rimmed baking sheets with parchment paper and then greases them well. Set aside.
Using an air popper, pop all the popcorn in shifts and dump it into a bowl large enough to hold all the popped corn with room to stir well. As you pop and dump, remove all the unpeopled kernels and any leftover shells and skins.
In a large saucepan over medium heat, melt the butter. Once it's melted, stir in the brown sugar, corn syrup, and salt. Slowly bring to a boil, stirring constantly. Once it reaches a low boil, reduce the heat to a medium-low simmer. Simmer for 3 minutes stirring frequently and until the sugar mixture begins to thicken.
Remove the pot from the stove and stir in the vanilla extract and baking soda. then carefully pour the caramel sauce over the popcorn and toss until it's well coated and mixed. Add the peanuts and stir until the peanuts and chocolate are mixed evenly throughout the popcorn, but the popcorn is not broken apart.
Spread the popcorn onto the baking sheets in even layers. Bake for 1 hour, stirring every ten minutes. Halfway through, switch the positions of the baking sheets, moving the top to the bottom and the bottom to the top. The popcorn will harden and turn a deeper caramel color as it bakes.
Turn the popcorn out onto the baking sheets, spreading into an even layer. Bake the popcorn for one hour, stirring and tossing every 20 minutes. Move the bottom tray to the upper rack and vice versa each time you stir. The popcorn will deepen in color and harden a bit as the caramel bakes and sets. Cool the popcorn to room temperature. Store in an airtight container. I’ve found the popcorn will keep, stored tightly, for 1-2 weeks.
Remove the trays and allow to cool on a baking sheet. If adding the chocolate aAbout five minutes after it comes out of the oven, toss the chocolate chips on the trays and mix. You want the chocolate to soften and melt a bit, but you also want to leave some chocolate chunks. Then cool for another hour. Store in an airtight container for 1 week.