Instructions

• Preheat the oven to 350°F (175°C). Line two rimmed baking sheets with parchment paper or silicone baking mats. If using parchment, lightly coat the parchment 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 evenly combined.
• Ensure the egg whites are at room temperature. Add 2 large egg whites and 1 tablespoon vanilla extract to the dry mixture and whisk just until the mixture is moistened and comes together into a thick, fudgy, brownie-like batter.
• If the batter appears too dry or crumbly, add a third large egg white and whisk to combine. If it still seems too thick, add the fourth egg white and whisk until the batter reaches a thick, fudgy consistency. Add egg whites one at a time; do not exceed the total of 4 egg whites.
• Gently stir in 1 1/2 cups bittersweet chocolate chips with a spatula until evenly distributed, taking care not to overwork the batter.
• Using a spoon or a spring-release cookie scoop, portion the batter into 12 evenly spaced mounds on each prepared baking sheet (24 cookies total, 12 per sheet).
• Bake the cookies for about 14 minutes, or until the tops are glossy and lightly cracked. Rotate the pans front-to-back halfway through baking if your oven heats unevenly.
• When done, remove the baking sheets from the oven and slide the parchment (with the cookies on it) onto wire racks. Let the cookies cool completely on the parchment before handling.
• Store cooled cookies in an airtight container for up to 3 days.