Preheat your oven to 350°F (175°C). Grease a baking pan.
In a mixing bowl, combine melted butter and sugar. Add eggs and vanilla extract, and whisk until smooth.
In another bowl, mix flour, cocoa powder, baking powder, and salt. Gradually add dry ingredients to the wet mixture, stirring until combined.
Pour half of the brownie batter into the prepared pan.
To make the caramel, heat sugar in a saucepan over medium heat, stirring constantly until it melts into a thick amber liquid. Add butter and stir until melted. Slowly pour in heavy cream while stirring. Let it boil for 1 minute, then remove from heat and stir in sea salt.
Pour the salted caramel over the brownie batter in the pan. Spread the remaining brownie batter over the caramel layer.
Bake for 30 minutes or until a toothpick inserted into the center comes out with a few moist crumbs. Let cool before cutting into squares.