Line a large baking sheet with aluminum foil; set aside.
Place the popped popcorn in a large bowl; set aside.
Melt butter in a small saucepan over medium-high heat.
Add brown sugar, corn syrup, and salt; stir until it starts to boil.
Let sugar mixture boil for about 2 minutes without stirring. (This will let it get nice and thick and caramel-y)
Add baking soda and vanilla. Stir until thoroughly combined.
Pour thickened caramel sauce over your popcorn. Use a spoon to toss and coat. (I found my caramel to be thicker/stickier than expected, so I recommend moving quickly; otherwise it will cool/harden, and it'll be impossible to coat your popcorn evenly.)
Spread popcorn over prepared baking sheet
Break candy bars into pieces and lay them randomly over your layer of popcorn.
Bake for 30 minutes. Take the tray out around the halfway mark to flip/toss your popcorn with a spatula to evenly distribute the melted chocolate onto each piece.
Remove, sprinkle with sea salt to taste and allow popcorn to cool completely.
Enjoy!
Recipe by Just Putzing Around the Kitchen at https://www.justputzing.com/2013/10/salted-dark-chocolate-caramel-corn.html