Prep the pan: Heat the oven to 350°F (175°C). Line an 8-inch square pan with parchment, leaving overhang for easy lifting. Lightly butter the parchment.

Melt the butter: In a medium, heatproof bowl, melt the butter gently in the microwave or over a saucepan of simmering water. You want it hot, not sizzling.

Whisk in sugars: Add granulated sugar and brown sugar to the hot butter. Whisk for 30–45 seconds until glossy and thick. This helps create that shiny top.

Beat in eggs and vanilla: Add the eggs one at a time, whisking well after each addition until the mixture looks smooth and slightly lighter. Stir in the vanilla.

Add cocoa and salt: Sift in the cocoa powder and salt. Whisk until fully combined and no streaks remain.

Fold in flour: Switch to a spatula and fold in the flour gently. Stop mixing as soon as the flour disappears. Overmixing can make brownies tough.

Stir in chocolate: Fold in the chopped chocolate (and nuts, if using). The batter will be thick and glossy.

Transfer to pan: Scrape the batter into the prepared pan and smooth the top. If you like, sprinkle a little flaky salt over the surface.

Bake: Bake for 20–25 minutes, until the edges are set and a toothpick inserted 2 inches from the edge comes out with moist crumbs. The center should look slightly underbaked—that’s perfect for fudgy texture.

Cool completely: Let brownies cool in the pan on a rack for at least 1 hour. Lift out with the parchment and cut into squares with a sharp knife. Wipe the knife between cuts for clean edges.