Collect dark chocolate, butter, sugar, eggs, flour, cocoa powder, salted caramel sauce, and sea salt.
Melt dark chocolate and butter together, creating a smooth mixture.
Whisk sugar and eggs until light and fluffy.
Mix the melted chocolate into the sugar and eggs.
Sift in flour and cocoa powder, folding until just combined.
Pour half the batter into a lined baking pan.
Drizzle salted caramel sauce over the batter.
Pour the remaining batter over the caramel layer.
Use a knife to swirl the batter and caramel for a marbled effect.
Bake until set, sprinkle with sea salt, cool, then cut into squares.