Preheat oven to 250°F.
Combine the popcorn, cashews, and pecans in a large baking pan or disposable pan. 12 cups plain popcorn, 1 cup cashews, 1 cup pecan halves
Place the butter, brown sugar, corn syrup and salt in a medium size pot and bring to a boil over medium heat.
1 cup unsalted butter, 2 cups brown sugar, 3/4 cup light corn syrup, 1 teaspoon kosher salt
When the syrup starts to boil continue to cook, undisturbed, until the temperature reaches 250°F on a candy thermometer, or about 5 minutes. Remove from the heat and stir in the baking soda, vanilla, pumpkin pie spice, and cinnamon until well blended.
1 teaspoon baking soda, 1 teaspoon vanilla extract, 1/2 teaspoon pumpkin pie spice, 1/2 teaspoon ground cinnamon
Pour the caramel mixture over the popcorn and using a large spoon, gently stir until evenly coated.
Bake for 1 hour, stirring and breaking up any clumps, every 15 minutes.
Remove from the oven and let cool completely before serving.