Preheat the oven to 350°F (177°C) and line a 9-inch square metal baking pan with parchment paper, leaving an overhang on two opposite sides to lift out the finished brownies (makes cutting easier!). Set aside.

In a small microwave-safe bowl or liquid measuring cup, combine the butter and half (2oz/56g) of the chopped chocolate. Melt in 30-second increments, stirring after each, until completely melted and smooth. Set aside to slightly cool while you continue.

In a large bowl with a handheld or stand mixer fitted with a whisk attachment, combine the sugar and eggs. Beat on medium-high speed until the sugar is dissolved and the mixture is pale and ribbon-y, about 3 minutes.

Pour the warm melted butter/chocolate into the bowl with the sugar/eggs, add the vanilla, and beat or whisk to combine.

With a fine-mesh sieve, sift the cocoa powder, flour, and salt into the batter, then whisk or beat on low speed to incorporate. Fold in the remaining 2 ounces/57g chopped chocolate and the chocolate chips. The batter will be very thick. Spread it evenly into the prepared pan. (A small offset spatula can help here.)

Bake for 28–30 minutes, then test the brownies with a toothpick. Insert the toothpick into the center of the pan. If it comes out coated with wet batter, the brownies are not done. If there are only a few moist crumbs, the brownies are done. Keep checking every 2 minutes until you have moist crumbs. Brownies typically take 30–32 minutes in my oven. Err on the side of under-baking, as the brownies will continue to set as they cool.

Remove from the oven and place on a cooling rack to cool completely in the pan. When cool, lift the brownies out by gripping the parchment overhangs and transfer to a cutting board. Use a sharp knife to cut into squares.

Cover and store leftover brownies at room temperature for up to 1 week.