Preheat your oven to 350°F (175°C). Grease an 8×8 inch square baking pan with butter or line it with parchment paper, leaving an overhang on the sides for easy removal later.
In a medium bowl, whisk together the melted butter and sugar. Add the eggs and vanilla extract, beating well until the mixture is smooth. Sift in the cocoa powder, flour, salt, and baking powder. Stir gently until just combined; do not overmix.
Spread the batter evenly into the prepared baking pan. Bake for 20 to 25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. Do not overbake, as you want the base to remain fudgy.
Remove the pan from the oven. While the brownies are still hot, immediately press the caramel corn gently into the top of the brownies. The residual heat will help the popcorn adhere to the surface.
Warm your caramel sauce slightly so it is pourable. Drizzle the caramel sauce generously over the popcorn layer. If using chocolate chips, melt them and drizzle them over the top as well. Let the brownies cool completely in the pan before slicing.