Ultra-rich, dense brownies with deep chocolate flavor from cocoa, melted chocolate, and chocolate chips, finished with shiny crackly tops and melt-in-your-mouth centers.
Preheat the oven to 350°F (177°C). Line a 9-inch square metal baking pan with parchment paper, leaving an overhang on two opposite sides for easy removal.
In a small microwave-safe bowl or liquid measuring cup, combine the butter and half (2 oz/56–57 g) of the chopped chocolate. Microwave in 30-second increments, stirring after each, until completely melted and smooth. Set aside to cool slightly.
In a large bowl using a handheld or stand mixer fitted with the whisk attachment, beat the sugar and eggs on medium-high speed until pale, thick, and ribbon-y, about 3 minutes.
Pour the warm melted butter/chocolate mixture into the bowl with the sugar and eggs, add the vanilla, and mix to combine.
Sift the cocoa powder, flour, and salt into the bowl, then mix on low speed just until incorporated.
Fold in the remaining chopped chocolate and the chocolate chips. The batter will be very thick.
Spread the batter evenly into the prepared pan (a small offset spatula helps).
Bake for 28–30 minutes, then begin checking doneness. Insert a toothpick into the center: if it comes out with wet batter, continue baking and check every 2 minutes. Brownies are done when the toothpick has a few moist crumbs, not completely clean (typically no more than about 32 minutes).
Place the pan on a wire rack and cool brownies completely in the pan. Use the parchment overhang to lift out, then slice into squares.