Preheat oven to 250°F Line 2 baking sheets with nonstick baking mats; set aside.
Pop popcorn according to package directions, get rid of unpopped kernels; set aside.
Make caramel: Combine butter, sugar, and corn syrup in a medium pot over medium heat. Cook, stirring occasionally until sugar has dissolved. Increase heat to medium-high, and cook, without stirring, until golden brown, about 5 minutes, swirling pot occasionally.
Remove mixture from heat and quickly stir in salt, vanilla, cinnamon & cayenne with a heatproof spatula or spoon. Immediately pour over popcorn mixture and stir to incorporate. Divide popcorn mixture evenly between baking sheets. Transfer to oven and bake, about 30 minutes, stirring occasionally.
Let cool on sheet pans before breaking apart into clusters. Store popcorn in an airtight container for up to 1 week.
*Note: If you opt for the ‘pepitas’ the pumpkin seeds instead of nuts (use one or the other not both) ~ you will need to toast the pumpkin seeds in a large skillet over medium-high heat, until browned and popping, tossing and stirring occasionally, about 4 minutes. (Do this in batches, if needed.) Then, add to the popcorn.
*If making popcorn balls, use following directions: When the popcorn is cool enough to handle, coat your hands with some butter and shape into 4-inch balls. Wrap in waxed paper and tie with a string, if desired. Serve or store covered at room temperature for up to a week.