Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan or line it with parchment paper for easy removal.
In a large mixing bowl, whisk together the melted butter and granulated sugar until well combined and slightly glossy.
Add the eggs one at a time, whisking well after each addition. Stir in the vanilla extract.
In a separate bowl, sift together the flour, cocoa powder, baking powder, and salt. Gradually fold the dry ingredients into the wet mixture until just combined. Avoid overmixing.
Gently fold in the semi-sweet chocolate chips.
Pour half of the brownie batter into the prepared baking pan and spread it evenly.
Drizzle half of the caramel sauce over the brownie batter, and use a toothpick or knife to swirl it into the batter slightly.
Pour the remaining brownie batter over the caramel layer and repeat the process with the remaining caramel sauce, swirling again for a marbled effect.
Bake in the preheated oven for 25-30 minutes or until a toothpick inserted into the center comes out with a few moist crumbs (but not wet batter).
Once done, remove from the oven and let cool in the pan for at least 15 minutes before cutting into squares.
For an optional touch, sprinkle a few flakes of sea salt on top before serving.
Notes
For an optional touch, sprinkle sea salt flakes on top before serving.