Grease an 8x8 inch glass baking dish with butter, and cut a strip of parchment paper so that it can lay flat across the bottom and overlaps two of the sides (these "handles" will allow you to lift the finished bars easily from the baking dish once cooled).
In a large, heavy bottomed pot, melt the butter over medium heat. Stir in the mini marshmallows, and just before the marshmallows completely lose their shape, add ¼ cup of the salted caramel sauce and stir until completely smooth. Remove the pan from heat, and mix in the popcorn. You’ll need to use some muscle and it may seem like you have too much popcorn, but just keep tossing it all together until well-combined. Add in the chocolate chunks, and stir until they are well-distributed. Don't worry if the chocolate melts a little bit - they will still be delicious!
Pour the popcorn and marshmallow mixture into the prepared baking dish. With wet hands (or through a piece of parchment paper), press the hot mixture together so that is fills the pan and is well-compacted. Allow to cool.
Once cool, lift the contents of the pan out of the baking dish and place on a cutting board. Drizzle with the remaining salted caramel sauce and cut into 2x2 inch squares. If desired, sprinkle each some edible gold star glitter for a bit of Old Hollywood glamour.
The Salted Caramel Popcorn Bars taste best the same day, while the popcorn is still fresh and crunchy. They can be stored in an airtight container for 2-3 days, but the popcorn will lose it’s crunch over time.