Preheat the oven to 350°F (180°C). Line an 8x8 inch metal baking pan with parchment paper, leaving overhang on two sides for easy lifting.
Combine the butter and chopped chocolate in a microwave-safe bowl. Microwave in 20-second increments, stirring after each, until fully melted and smooth.
Whisk both sugars into the hot butter and chocolate mixture until fully combined, for around 1 minute.
Add the eggs one at a time, and vanilla, and whisk for about 3 minutes, until smooth and glossy.
Sift the cocoa powder and salt over the batter and fold to combine. Add the flour and fold until just combined. Don't overmix. Fold in chocolate chips if using.
Scrape the batter into the prepared pan and smooth the top.
Bake for 28 to 32 minutes, until the top is set and shiny, and a skewer inserted into the centre comes out with a few moist crumbs (no wet batter). Don't overbake.
Cool the brownies completely in the pan on a wire rack before lifting out and slicing. For very clean cuts, chill in the fridge for an hour, then slice with a sharp knife, wiping it clean between cuts.
Notes
Notes
Both US customary and metric measurements are provided. Use the toggle to switch between the two.
Use a good quality semi-sweet chocolate with real cocoa butter, not compound chocolate.
Use room temperature eggs. If yours are cold, sit them in warm water for 5 minutes.
These brownies don't have leavening, so they're very forgiving and hard to overbake into a cakey texture.
Store at room temperature in an airtight container for up to a week, or freeze the whole slab for up to 3 months. Thaw at room temperature.
For an extra crinkley top: whisk the eggs and sugars separately first until thick and pale, then add the (cooled) melted chocolate mixture and continue with the recipe.