Instructions

• Preheat the oven to 350°F. Line two rimmed baking sheets with parchment paper or silicone mats; if using parchment, lightly coat it with nonstick spray.
• In a large bowl, whisk together 3 cups powdered sugar, 2/3 cup Dutch-process cocoa powder, and 1/4 teaspoon salt until uniform.
• Make sure the large egg whites are at room temperature. Add 2 large egg whites and 1 tablespoon vanilla extract to the dry ingredients and whisk (or beat) just until the mixture is moistened and comes together.
• Assess the texture: you want a thick, fudgy, brownie-like batter. If it seems too dry or too stiff to scoop, add one more egg white and mix until incorporated. If still too thick, add a fourth egg white and mix—do not exceed 4 egg whites.
• Gently fold in 1 1/2 cups bittersweet chocolate chips until evenly distributed.
• Using a spoon or a spring-release cookie scoop, portion the batter into 12 evenly spaced mounds on each prepared baking sheet (12 mounds per sheet).
• Bake in the preheated 350°F oven for about 14 minutes, until the tops are glossy and lightly cracked.
• Remove the baking sheets from the oven and immediately slide the parchment (with the cookies on it) onto wire racks.
• Let the cookies cool completely on the racks before removing them from the parchment.
• Store cooled cookies in an airtight container for up to 3 days.