Line a very large sheet pan with foil or wax paper and set aside.
Prepare the popcorn using whatever method you prefer (see note 2). Measure out 16 cups, taking care to remove all unpopped kernels; add to the large paper bag.
Combine butter, syrup, sugar, and salt in a fairly large bowl. Microwave for 3 minutes, stirring after each minute, to form a thick mixture.
Combine the baking soda and vanilla in a small bowl. Stir this mixture and pour over the butter, sugar, and syrup mixture; stir to create the foam.
Quickly pour the foaming mixture over the popcorn, fold the top of the bag over, and shake very well to distribute the syrup over the kernels.
Place the bag (with the top folded over) in the microwave and heat on high for 1 minute. Remove and shake well again. Repeat this step (microwave for 1 minute, remove, and shake the bag). Then microwave for 1 minute longer. That will be a total of 3 one-minute microwave blasts, with 2 shakes in between.
Empty the coated popcorn onto the foil-lined baking sheet. Spread it loosely over the surface, leaving clusters grouped together. Let cool until it firms up and dries. Enjoy!
Video
Notes
Note 1: For this recipe, you’ll need a large brown paper bag—so save one when shopping if you can! If they’re hard to find, you can order a pack online. Or use these giant brown paper lunch sacks—just halve the recipe if you go this route.Note 2: A few options for popcorn:
If purchasing already popped popcorn, this recipe comes together a bit quicker, but it’s quite a bit more spendy.
If using microwave popcorn packets, try to use a brand with the fewest seasonings, not the movie-theater mega-butter type. Servings vary by the brand, from 8–12 cups. To be on the safe side, use 2 bags. (Here’s my favorite packet popcorn.)
You can also make microwave popcorn from your own kernels. Place 1/4 cup kernels and a teaspoon of vegetable oil in a paper bag (the size of a lunch bag) and fold the top over twice. Microwave for about 2-1/2 minutes to 3 minutes–until the popping slows to about one pop per 2 seconds. Don’t overcook or you’ll have burned popcorn. Make 4 bags for this recipe.
If making popcorn on the stove, use about 1 cup of kernels. You may end up with some extra popcorn, but I’m sure someone will help you use it up!
Storage: Store leftovers in an airtight container at room temperature for up to 3 days. For longer storage, freeze in a sealed bag for up to 3 months.