1/2 cup popcorn kernels (10 to 12 cups popped)
1 teaspoon pumpkin pie spice, store-bought or homemade
1/2 teaspoon kosher salt
1/4 teaspoon baking soda
3/4 cup (6 ounces) unsalted butter
1 cup light brown sugar, packed
1 teaspoon vanilla extract
→ For Step-by-Step Photos: How To Make the Best Caramel Popcorn
Heat the oven to 250°F. Line two baking sheets with parchment or nonstick baking mats. Mix together the pumpkin spice, salt, and baking soda and set near the stove.
Pop the popcorn on the stovetop, in the microwave, or using your preferred method. You should have 10 to 12 cups of popped popcorn. Transfer the popcorn to a large, heat-proof mixing bowl and set near the stove.
Melt the butter in a 2-quart or larger sauce pan on the stovetop. Do not use a smaller pot; the sugar mixture will boil over the sides. Once melted, stir in the brown sugar. Increase the heat to medium-high and bring the butter-sugar mixture to a boil. Once boiling, boil for 3 to 4 minutes or until the sugar mixture reaches approximately 275°F.
Remove the pan from heat and stir in the vanilla, pumpkin pie spice, salt, and baking soda. The mixture will bubble up immediately and double in size; be very careful to avoid splatters. Stir the mixture until the spices are incorporated and you make a smooth sauce.
Pour 1/4 of the sauce over the popcorn and stir to combine. Continue pouring a bit of the sauce and stirring until all the sauce has been stirred into the popcorn. Divide the popcorn between the baking sheets and spread into an even layer.
Bake the popcorn for 1 hour, stirring every 15 minutes. Because of the spices added, the coating will look matte instead of glossy. Baking the popcorn makes the caramel corn extra-crunchy. At the end of the hour, break apart any clumps of popcorn with your fingers and let cool.
Popcorn is at its best and most addictive when just cooled from the oven, but will stay crunchy if kept in an airtight container at room temperature for several days.