Preheat your oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper.

In a double boiler or microwave-safe bowl, combine the butter and dark chocolate. Heat gently, stirring continuously until melted and smooth, about 2-3 minutes.

In a large mixing bowl, whisk together the eggs, granulated sugar, and brown sugar until the mixture is smooth and slightly thickened, about 2-3 minutes.

Mix in the vanilla extract and the melted chocolate mixture into the egg-sugar blend; gently fold until fully incorporated.

Gradually incorporate the all-purpose flour into the chocolate mixture, stirring until just combined.

Pour half of the brownie batter into the prepared pan, spreading it evenly. Spoon dollops of salted caramel sauce on top.

Spread the remaining brownie batter over the caramel layer and create gentle swirls with a knife or toothpick.

Bake for 25-30 minutes, until a toothpick inserted in the center comes out with moist crumbs.

Sprinkle flaky sea salt over the top as soon as brownies come out of the oven. Let them rest before transferring to a wire rack to cool completely.

Once cooled, cut into squares to reveal the swirls of caramel throughout the brownies.