Line your 9x13-inch baking pan with parchment paper or lightly grease it to prevent sticking. Preheat your oven to 350°F (175°C).
In a large mixing bowl, pour in the melted unsalted butter. Add granulated and brown sugar. Whisk together until fully combined and smooth.
Crack in the eggs one at a time, whisking well after each addition. Stir in the vanilla extract.
In a separate bowl, sift together the all-purpose flour, unsweetened cocoa powder, baking powder, and salt.
Gradually add the dry ingredients to the wet ingredients. Use a rubber spatula to fold gently until just incorporated. Avoid overmixing.
Add the semi-sweet chocolate chips and fold them in evenly.
Pour half of the brownie batter into the prepared pan and spread evenly. Drizzle half of the salted caramel sauce over the batter. Pour the remaining batter on top and smooth it out. Swirl the remaining caramel sauce over the top.
Bake for 35-40 minutes. Check doneness with a toothpick; a few moist crumbs are perfect. Remove from oven and sprinkle sea salt over the top while warm. Cool completely on a cooling rack before cutting.