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

Melt butter and chocolate: In a heatproof bowl, melt the butter and chopped chocolate together. Do this in short 20–30 second bursts in the microwave, stirring between bursts, or over a double boiler. Stir until smooth and glossy.

Add sugars: Whisk in the granulated and brown sugars while the mixture is still warm. It will look thick and a bit grainy—that’s fine.

Beat in eggs and vanilla: Add the eggs one at a time, whisking well after each until the batter looks satiny. Whisk in the vanilla. This step helps build that crackly top.

Fold in dry ingredients: Sift or whisk the cocoa, flour, and salt in a separate bowl, then add to the wet mixture. Use a spatula to fold just until no dry spots remain. Do not overmix.

Stir in extras: If using chocolate chips or nuts, fold them in gently. For a peanut butter swirl, dollop a few spoonfuls over the batter and drag a knife through once or twice.

Bake: Spread the batter evenly in the pan. Bake for 22–28 minutes if using an 8-inch pan, or 18–24 minutes for a 9-inch pan. Pull them when the center is just set and a toothpick comes out with a few moist crumbs.

Cool and slice: Let the brownies cool in the pan for at least 30–45 minutes. Lift out using the parchment and slice with a sharp knife. For cleaner edges, chill for 30 minutes before cutting.