01 -
Line an 8-inch square baking pan with parchment paper, leaving an overhang on the sides, and lightly grease the edges.
02 -
Combine unsalted butter and chopped semi-sweet chocolate in a heatproof bowl. Melt over a simmering water bath or in the microwave in short intervals, stirring until smooth and glossy. Allow to cool for 2 to 3 minutes.
03 -
Whisk granulated sugar and light brown sugar into the melted chocolate mixture until the surface appears shiny. Add eggs one at a time, whisking thoroughly after each addition to create a thick batter. Incorporate vanilla extract.
04 -
Sift all-purpose flour, cocoa powder, and fine sea salt directly into the bowl. Fold gently with a spatula until just combined with no visible dry streaks.
05 -
Gently fold in raspberries, keeping them frozen if using frozen fruit. Sprinkle chocolate chips over the batter if desired.
06 -
Spread the batter evenly into the prepared pan.
07 -
Bake in a preheated oven at 350°F for 25 to 32 minutes, until a toothpick inserted into the center emerges with a few moist crumbs attached.
08 -
Place the pan on a wire rack and let cool for at least 1 hour. Use the parchment overhang to lift the baked slab out and cut into portions with a warm knife for clean slices.