Preheat the oven to 350°F.
Grease a 9x13-inch baking pan and line it with parchment paper.
Add the dark chocolate and butter to a heatproof bowl.
Melt them over a pot of simmering water, stirring until smooth.
Let it cool for a few minutes before moving on.
Whisk the eggs and sugar in a separate bowl until thick and pale.
Use a hand whisk or electric mixer—whatever you like.
Pour the melted chocolate-butter into the egg-sugar mixture.
Fold gently until just blended.
Sift in flour and salt, then fold carefully.
Add the chocolate chunks and mix until everything’s just combined.
Don’t overmix—really, just stop when it looks mixed!
Pour the batter into the prepared pan and smooth out the top.
Bake for 25 to 30 minutes, or until a toothpick poked in the center comes out with a few moist crumbs.
Let the brownies cool in the pan before slicing.