Pop your popcorn using your preferred method and transfer it to a large mixing bowl, removing any unpopped kernels as you go. Lightly salt the popcorn if it's unsalted, tossing gently to distribute.

Add sugar, corn syrup, water, butter, and salt to your saucepan over medium heat. Stir constantly until the butter melts and the sugar completely dissolves, which takes about 3 minutes. Watch for the mixture to turn clear before moving to the next step.

Clip your candy thermometer to the side of the pan and stop stirring once the mixture begins to boil. Cook without stirring until the temperature reaches 250°F (hard ball stage), which takes 6 to 8 minutes.

Remove the pan from heat immediately when it hits 250°F and stir in the vanilla extract and baking soda. The mixture will bubble up vigorously, expanding in volume, so use caution and keep your face back from the pan.

Pour the hot syrup over the popcorn in a thin stream while stirring with a wooden spoon. Continue stirring and folding for about 2 minutes until every kernel gets coated with the glossy syrup.

Let the coated popcorn sit for 2 to 3 minutes until it's cool enough to handle but still warm and pliable. Test by touching a small piece; it should feel very warm but not burning hot.

Coat your hands generously with butter or cooking spray and scoop about 1 cup of the mixture into your palms. Press firmly to compact the popcorn into a tight ball, squeezing and rotating to create a smooth, round shape. Re-grease your hands between every 2 or 3 balls to prevent sticking.

Place each shaped ball on your prepared baking sheet, spacing them so they don't touch. Allow them to cool at room temperature for at least 15 minutes until the coating hardens completely.