Preheat oven to 250º F. Line a baking sheet with parchment paper.

Heat the oil in a 3-quart saucepan on medium-high heat. Put 3 or 4 popcorn kernels into the oil and cover the pan. When the kernels pop, add the rest of the popcorn kernels in an even layer. Cover, remove from heat and count 30 seconds. (This method first heats the oil to the right temperature, then waiting 30 seconds brings all of the other kernels to a near-popping temperature so that when they are put back on the heat, they all pop at about the same time.)

Return the pan to the heat. The popcorn should begin popping soon, and all at once. Once the popping has begun, gently shake the pan by moving it back and forth over the burner. Keep the lid slightly ajar to let the steam from the popcorn release; this makes the popcorn slightly drier and crisper. Once the popping slows to several seconds between pops, remove the pan from the heat.

Coat a large mixing bowl with non-stick cooking spray, and transfer the popcorn from the pan to the bowl, taking care to pick out and discard any unpopped kernels.

In a medium saucepan, whisk together the brown sugar, corn syrup, butter, salt, spices and water. Bring to a simmer over medium-high heat. Continue to simmer, whisking often, until the mixture reads 250º F on a candy thermometer, about 3 to 4 minutes. Immediately remove the pan from the heat, and whisk in the baking soda and vanilla.

Quickly pour the hot caramel over the popcorn. Use a rubber spatula to gently fold the caramel into the popcorn, taking care to distribute it as evenly as you can. Stir in the cashews, and transfer the mixture to the prepared baking sheet. Bake for 1 hour, stirring and turning the popcorn with a spatula every 20 minutes. Remove from the oven, and place on a cooling rack for 20 minutes. Gently break up the popcorn, and serve.

Keep in an airtight container for up to 5 days.