Preheat oven to 225 F. Place oven rack in the center of the oven.
Line a large (sheet pan) or two smaller baking sheets (half sheet pans) with parchment paper or silicone baking mats.
Add popcorn mix ingredients to baking sheet(s) in a single layer. Set aside.
To make the caramel, combine caramel ingredients in a large saucepan.
Cook over medium heat, whisking constantly, until mixture comes to a boil.
Continue cooking, whisking constantly, for 3 minutes.
Pour caramel over popcorn mix ingredients. Don't worry if everything isn't covered.
Bake for 15 minutes. If entire mix won't fit on middle rack, bake one tray at a time. I've found that the caramel will burn if it's closer to the heating elements.
Stir, and continue to bake another 15 minutes. Repeat this process for a total baking time of 60 minutes.
Stir one final time.
Let mix cool to room temperature, and break into pieces.
Notes
*I like to use a mix of plain Cheerios and Rice or Corn Chex.**Can sub another type of nut or 1 more cup cereal, pretzels, or popcorn. ***Nutrition values are estimates.