In a saucepan over medium heat, melt 80 g of butter, stirring occasionally. Continue cooking until it turns golden brown and smells nutty. Remove from heat and let it cool for a few minutes.

In a mixing bowl, combine the browned butter with 80 g brown sugar, 40 g granulated sugar, and 1 g salt. Mix well until smooth.

Add 1 egg and 2 g vanilla extract. Whisk until fully incorporated.

Fold in 85 g all-purpose flour and 70 g chocolate chips until just combined. Don’t overmix.

Place the dough in the fridge to chill while preparing the brownie layer.

Preheat the oven to 329°F (165°C). Line an 8x8-inch baking pan with parchment paper, leaving overhang for easy removal.

In a heatproof bowl, melt 180 g butter and 320 g chocolate over a double boiler (or microwave in intervals). Stir until smooth. Let it cool slightly.

In another bowl, whisk 180 g granulated sugar, 80 g brown sugar, and 4 eggs. Whisk vigorously for 2–3 minutes until the mixture is light, thick, and pale—this is the key to that signature crackly top.

In a separate bowl, sift together 120 g flour, 50 g cocoa powder, and 2 g salt.

Add the melted chocolate-butter mix to the whipped eggs and sugars. Stir until combined.

Gently fold in the dry ingredients until just incorporated. Fold in 120 g chocolate chunks if using.

Spread half the brownie batter evenly into the lined baking pan.

Drop spoonfuls or chunks of the chilled cookie dough across the brownie layer.

Pour the remaining brownie batter on top and spread to cover.

Add more chunks of cookie dough on top and finish with extra chocolate chunks.

Bake for 45–55 minutes, or until the edges are set and a toothpick inserted into the center comes out with moist crumbs.

Cool completely in the pan before slicing. This step is crucial for clean edges and gooey centers.