Start by melting the butter and chopped chocolate together in a heatproof bowl over a pot of simmering water, or use the microwave in short bursts.
In a large mixing bowl, whisk together the granulated sugar, brown sugar, and eggs until the mixture looks pale and slightly thickened.
Pour the cooled chocolate-butter mixture into the bowl with the eggs and sugar. Stir until everything is well blended.
In a separate bowl, sift together the flour, cocoa powder, and salt. Gently fold the dry ingredients into the wet mixture, being careful not to overmix.
Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, leaving a little overhang so you can lift the brownies out later.
Pour the batter into the pan and spread it evenly.
Bake for 30–35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Let the brownies cool in the pan for at least 20–30 minutes before slicing.
