Preheat your oven to 250°.
Spray a large sheet pan with non-stick spray, line it with parchment paper, and spray it again.
Get your baking soda (NOT baking powder! Check that label!), vanilla, and peanuts measured and put to the side, ready for their big moments! Once the caramel is ready, things move very fast!
Pop all your popcorn, put in in a very large bowl, big enough for assertive stirring in a just a bit.
In a small saucepan, combine brown sugar, corn syrup, molasses, butter, and salt. Cook over medium high heat, whisking constantly, until temperature reaches 250° with a thermometer or about 2 minutes after bubbles first appear.
Take the caramel off the heat and immediately whisk in the vanilla and baking soda. It will bubble and pop! Just letting you know 😉
Pour over the popcorn, using a rubber spatula to get all the caramelly goodness out of the pan, add the peanuts (if using) and stir stir stir to evenly coat the popcorn with caramel.
Pour onto your prepared baking sheet and spread evenly with the spatula. Bake for 20 minutes, stir, bake for another 20 minutes, stir, and bake for a final 20 minutes.
Remove from the oven and stir one last time, then place on a cooling rack until completely cooled.
This would last up to one week in a tightly covered container or ziplock bag if you didn’t just eat it all, but you did.