Chop the butter. Throw the pieces in a saucepan or microwave-safe bowl with chopped chocolate.
Hit it in your microwave for 20-second bursts, stirring after every burst until melty. Let it cool for about five minutes.
Preheat your oven to 350°F. Line a 9" square pan with parchment paper, covering the sides as well. Set it aside.
Whisk brown and granulated sugars into the butter/chocolate mix. Add eggs + vanilla, whisking until smooth.
Mix in cocoa powder, flour, and a pinch of salt until you don't see any dry bits. Gently fold in your chocolate chips.
Spread this batter into your prepared pan and bake for around 32 to 35 minutes. Test them after 30 minutes with a toothpick. A bit of underbaking is fine because they will keep cooking while cooling.
Cool them on the wire rack for an hour or two. Use the overhung parchment paper to lift them off the pan.