INGREDIENTS
•
16 tablespoons (1 cup) unsalted butter, cut into small cubes
•
2 1/2 cups granulated sugar
•
3/4 cup Dutch-process cocoa powder
•
3/4 cup black cocoa powder (or an additional 3/4 cup Dutch-process)
•
1/2 teaspoon salt
•
2 teaspoons vanilla extract
•
4 large eggs
•
1 cup all-purpose flour
•
6 ounces coarsely chopped semisweet or bittersweet chocolate (about 1 1/3 cups), divided