Line a baking sheet with parchment paper and place the popcorn in an extra large bowl. Set both aside.
190 grams popped popcorn
Add the brown sugar, butter, corn syrup, and cocoa powder to a large microwave safe bowl. Mix well and heat on high for 3 minutes.
½ cup brown sugar, ½ cup unsalted butter, ¼ cup light corn syrup, ¼ cup unsweetened cocoa powder
Remove the bowl from the microwave and stir. The mixture should be boiling. If not, place the bowl back in the microwave and continue to heat on high in 30-second intervals until the mixture comes to a boil.
Stir in the vanilla extract and salt (if using).
1 teaspoon pure vanilla extract, Sea salt
Pour the butter/sugar mixture over the popcorn and use a rubber spatula to stir the popcorn until it is evenly coated.
Spread the coated popcorn in an even layer onto the prepared baking sheet.
Let the popcorn cool at room temperature for 2 hours before serving or packaging.