Begin by popping 4 quarts of fresh popcorn using an air popper or stovetop method. Once popped, spread the popcorn into a large roasting pan, ensuring an even layer for better coating. Keep the popcorn warm by placing it in an oven preheated to 250°F as you prepare the syrup.

In a heavy saucepan, combine 1 cup of granulated sugar, 1 cup of brown sugar, 1/4 cup of water, 1/4 cup of light corn syrup, 1 tablespoon of white vinegar, and 1/4 teaspoon of salt. Heat the mixture over medium heat, stirring until the sugars dissolve completely and the mixture reaches a gentle boil.

Continue cooking the syrup, stirring occasionally, until it reaches the hard-ball stage at approximately 260°F. Use a candy thermometer for accuracy. The syrup will turn a lovely golden color.

Once your syrup has reached the correct temperature, promptly remove the saucepan from heat. Stir in 1/2 cup of unsalted butter until melted and fully combined. Then, add green food coloring to the mixture and mix until well incorporated.

Drizzle the warm green syrup over the popcorn in the roasting pan. Using a large spatula or wooden spoon, gently toss the popcorn to ensure even coating.

Spread the coated popcorn back on the parchment-lined surface or allow it to cool in the roasting pan. Let the mixture cool completely for about 15-20 minutes before breaking it into pieces.

Store your St. Patrick's Day Popcorn in an airtight container at room temperature to maintain its delightful crunch.