01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a medium saucepan over medium heat, melt sugar while stirring constantly until amber-colored. Add cubed butter and whisk until melted. Remove from heat, carefully whisk in heavy cream (it will bubble), then stir in flaky sea salt. Allow to cool to room temperature.
03 - In a large bowl, whisk melted butter with granulated and brown sugars until smooth. Incorporate eggs and vanilla extract, mixing until glossy.
04 - Sift together all-purpose flour, cocoa powder, and sea salt. Fold dry ingredients into wet mixture until just combined. Stir in chopped dark chocolate.
05 - Pour batter into prepared pan and smooth the surface. Drizzle cooled salted caramel over batter and gently swirl with a knife or skewer to create a marbled effect.
06 - Bake for 28 to 32 minutes until a toothpick inserted comes out with a few moist crumbs.
07 - Allow brownies to cool completely in the pan before cutting into 12 squares.