Instructions

• Place a rack in the center of the oven and preheat to 350°F (175°C). Line two baking sheets with parchment paper or silicone mats.
• In a small bowl, sift together ½ cup all-purpose flour, ⅓ cup unsweetened cocoa powder, ½ teaspoon salt, and ¼ teaspoon baking powder. Set aside.
• Set a heatproof bowl over (not touching) a saucepan of simmering water. Add 6 ounces coarsely chopped bittersweet chocolate and 4 tablespoons butter (cut into 6 pieces). Heat, stirring occasionally, until the chocolate and butter are mostly melted.
• Remove the bowl from the saucepan and stir until the chocolate and butter are completely melted and the mixture is smooth and glossy. Let the chocolate mixture cool to room temperature.
• In the bowl of a standing mixer fitted with the paddle attachment, or in a large mixing bowl with a hand mixer or whisk, beat 2 large room-temperature eggs and ⅔ cup granulated sugar on medium-high speed for about 2 minutes, until pale and foamy.
• Add 1 teaspoon pure vanilla extract and beat briefly to combine. Scrape down the bowl.
• Reduce the mixer speed to low and add the cooled chocolate-butter mixture. Mix just until incorporated. Scrape down the bowl.
• With the mixer still on low, gradually add the sifted dry ingredients and mix only until the dry ingredients are just incorporated and no streaks of flour remain. The batter will be thick, shiny, and brownie-like.
• Using a rubber spatula, gently fold in 12 ounces semisweet chocolate chips (about 2 cups) by hand until evenly distributed.
• For small cookies (~2-inch), drop rounded tablespoonfuls of dough onto the prepared baking sheets, leaving about 1 inch between mounds. For larger cookies (~3-inch), drop mounds of about 2 tablespoons of dough, leaving about 2 inches between mounds. If using, sprinkle a small pinch of flaky sea salt on top of each mound.
• Bake one sheet at a time in the center of the oven: 9 minutes for small cookies or 10 minutes for larger cookies. The tops should look slightly dry while the centers remain soft.
• Remove the baking sheet from the oven and let the cookies rest on the sheet for 2 minutes. Then transfer the cookies gently to a cooling rack to cool to room temperature.
• Repeat with the remaining dough, baking one sheet at a time. If you reuse the same baking sheet, allow it to cool completely between batches.