Pop the popcorn with an air popper or on the stove with oil. Place popped popcorn in a large bowl.

Cover one to two sheet pans with aluminum foil.

In a large saucepan, combine sugar, rum, butter, vanilla, and salt. Heat over medium heat, stirring very often. (See Rachel’s note above – just keep stirring – it gets dry-ish looking before it melts and looks like you’ve screwed things up!) Continue to cook until sugar melts and caramel becomes a dark caramel color. I takes about 15-20 minutes. Once it melts and turns a dark caramel color, act fast because it scorches quickly.

Add the baking soda and keep stirring. Be careful as 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 ten minutes before digging in.