Pop the popcorn using an air popper (or on the stove with oil if you don’t have an air popper). Place popped popcorn in a very large bowl (or two bowls). You’ll want enough room for stirring after you pour the caramel over it.
Cover one to two (I use two) sheet pans with aluminum foil.
In a large saucepan, combine sugar, rum, butter, vanilla, and salt. Heat over medium heat, stirring very often (I stir nearly continuously). Continue to cook until sugar melts and caramel becomes a pretty brown (caramel) color. If you’ve never made caramel, you’ll think you screwed this up. I did. It gets sort of dry-ish before it melts. Just keep stirring. Good things will happen. It takes about 15-20 minutes. Once it melts and turns a dark caramel color, trust your gut and act fast because it scorches quickly.
Add the baking soda (Measure it first and put it in a little bowl so you can add it all at once) and keep stirring. Be careful because it bubbles up quickly and almost doubles in quantity. Quickly remove from heat, pour over the popcorn and stir quickly to coat all the corn.
Spread the caramel corn out on foil lined sheet pans and allow to cool at least 10 minutes before digging in.
Try not to eat this all in one sitting. Let me know if you’re successful. You might want to share with friends!
Read entire recipe before starting, so you are prepared.