Preheat the oven to 200 degrees. Following the product instructions, pop the popcorn. When cool enough to handle, remove and discard any un-popped kernels. In a large saucepan, combine the butter, brown sugar, salt, 25 Star Balsamic Vinegar and syrup. Bring to a boil and stir until all ingredients are combined. Remove from the heat and stir in the baking soda (the mixture will foam up.)
Pour the mixture over the popcorn and toss to coat. Spread the popcorn mixture evenly onto a baking pan and cook for 1 hour, stirring every 15 minutes. Spread onto wax paper to dry.
Adapted from Sauce Magazine.