Line your counter or a large baking sheet with wax or parchment paper. Pop enough popcorn to yield about 10 cups and place in a large bowl.

In a microwave-safe bowl, combine 1/2 cup of unsalted butter, 1 cup of packed light brown sugar, and 1/4 cup of light corn syrup. Microwave on high for 1 minute, then stir thoroughly and return for another 2 minutes until bubbling.

Stir in 1 teaspoon of vanilla extract and 1/2 teaspoon of baking soda to the caramel mixture.

Pour the hot caramel mixture over the popped popcorn, stirring to coat evenly. Let it cool for about 5 minutes.

Grease your hands with butter and shape the caramel-coated popcorn into 2-inch balls, adding any optional mix-ins as desired.

Allow the popcorn balls to cool completely on the lined surface, then store in an airtight container or wrap individually in plastic wrap.