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 medium saucepan, melt the butter over low heat. Remove from heat and stir in the granulated sugar and brown sugar until combined.
Add the eggs one at a time, mixing well after each addition. Then stir in the vanilla extract.
In another bowl, whisk together the flour, cocoa powder, baking powder, salt, and instant coffee granules. Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Fold in the chocolate chips. Pour half of the brownie batter into the prepared baking pan, spreading it evenly.
Drizzle half of the salted caramel sauce over the first layer of batter. Pour the remaining brownie batter on top and swirl it with a knife to create a marbled effect.
Drizzle the remaining salted caramel sauce over the top and sprinkle sea salt flakes for garnish.
Bake for 25-30 minutes or until a toothpick inserted in the center comes out with a few moist crumbs.
Allow the brownies to cool in the pan for at least 15 minutes before cutting them into squares.
Notes
Serve on a rustic wooden platter, drizzled with additional salted caramel sauce and a sprinkle of sea salt.