Use an air-popper if you have one; don't add oil or butter to the popcorn while popping.
An air popper works best; however, an alternative would be to use a microwave; microwavable plain popcorn can be purchased in most grocery stores.
Once the popcorn is ready, spread onto two baking sheets to cool; add the pretzels; set aside.
Pre-heat the oven to 250°F.
In a large sauce pan, on medium heat, bring the brown sugar, corn syrup, pumpkin spice and butter to a boil.
Swirl the pan to ensure the ingredients are mixing together and the brown sugar is dissolving.
Once the mixture comes to a boil, continue cooking for exactly two minutes.
Remove the sauce pan from the heat and sit it into the kitchen sink; place the sauce pan in the sink to prevent possible overlfow when adding the baking soda; be careful as this caramel mixture is extremely hot.
Add the baking soda; stir well with a wooden spoon.
Poor half of this mixture over the popcorn in each of the baking sheets.
Sprinkle with salt, and, using metal tongs, toss gently to coat.
Place the sheets in the pre-heated oven and bake for 1 hour.
Remove the popcorn from the oven every 15 minutes; toss and place back in the oven.
Once done, remove from the oven and remove the popcorn from the baking sheet; try to keep the popcorn in a single layer on parchment paper that’s been spread out on a large table.
Allow to cool completely at room temperature; this will not take too long; about 30 minutes is good.
Once completely cooled, package or serve immediately.
