Line a baking sheet with parchment paper and set it aside. Place 190 grams popped popcorn (about 24 cups) in an extra-large bowl.

In a large microwave-safe bowl, combine ½ cup brown sugar (107 g), ½ cup slightly melted unsalted butter (113 g), ¼ cup light corn syrup (78 g), and ¼ cup unsweetened cocoa powder (21 g). Stir until the mixture is evenly combined.

Microwave the bowl on high for 3 minutes.

Carefully remove the bowl (it will be hot) and stir. The mixture should be boiling or bubbling. If it is not boiling, return the bowl to the microwave and heat on high in 30-second intervals, stirring after each interval, until the mixture is boiling.

Stir in 1 teaspoon pure vanilla extract (4 g) and sea salt to taste, if using.

Immediately pour the hot butter/sugar/cocoa mixture over the popcorn. Use a rubber spatula to gently fold and stir the popcorn until the kernels are evenly coated.

Spread the coated popcorn in an even layer on the prepared parchment-lined baking sheet.

Let the popcorn cool at room temperature for 2 hours before serving or packaging.