Start by popping your popcorn. You can use an air popper or the stovetop method. Once popped, place the popcorn in a large mixing bowl and set aside.
In a medium saucepan, combine the slightly melted unsalted butter, brown sugar, light corn syrup, unsweetened cocoa powder, and pure vanilla extract. Stir over medium heat until the mixture comes to a gentle boil. Allow it to boil for about 4-5 minutes without stirring.
Once the chocolate mixture has thickened slightly, remove it from heat. Carefully pour the hot chocolate mixture over the popped popcorn and gently fold them together until all the popcorn is coated evenly. If desired, sprinkle in some sea salt.
Preheat your oven to 250°F (120°C). Spread the coated popcorn evenly onto a baking sheet lined with parchment paper. Bake for about 30 minutes, stirring every 10 minutes.
After baking, remove the popcorn from the oven and let it cool completely. Once cooled, break it into clusters and store it in an airtight container.
