Preheat the oven to 250º F. Line two large sheet pans with parchment paper.
Melt the butter in a medium pot.
Add the pumpkin puree, brown sugar, corn syrup, pumpkin spice and salt. Mix it all together, then bring it to a boil. Boil it for 5 minutes without mixing it.
Remove the pot from the heat, and add the baking soda. Mix it well. It will foam up a little and lighten in color.
Slowly pour the caramel over the popcorn while mixing the popcorn. Mix until the popcorn is evenly coated.
Divide the popcorn between the two large sheet pans. Bake in the oven for 1 hour, stirring every 15 minutes.
Let the popcorn cool, then break it into pieces. Enjoy!
