Begin by popping the popcorn.  In a large heavy pot with a tightly fitting lid, heat the oil over medium heat.  Drop in three corn kernels and cover the pot.  Once you hear those three kernels pop, pour in the remaining popcorn and cover the pot again. Cook the popcorn over medium heat, making sure to swirl the corn kernels around in the pot as they cook and pop to keep them from burning.  Once the pops have slowed down, turn the heat off and pour the popcorn into a bowl. Add in the cashews and mix to evenly combine.

Preheat the oven to 250 degrees F.  In a large, heavy bottomed saucepan, melt the butter over medium heat.  Stir in the corn syrup, sugar, and 1/2 teaspoon salt.  Cook until the sugar dissolves, stirring only once or twice.  Raise the heat to high, and bring the mixture to a boil without stirring.  Keep heating the mixture until a candy thermometer reads 248 degrees F, about 3-5 minutes.  Remove the caramel sauce from the heat and stir in the baking soda.

Pour the caramel sauce over the popcorn mixture, stirring quickly to evenly coat all the popped popcorn and nuts.  Divide the popcorn mixture among two sheet pans and bake them for 45 minutes, stirring twice during the baking time.  You'll know the popcorn is ready if the caramel sauce crisps quickly upon being removed from the oven.  Immediately sprinkle on the remaining salt, and let the popcorn cool completely before serving.  Enjoy!