Preheat the oven to 350°F. Line a baking sheet with parchment paper and coat it lightly with cooking spray.
In a large bowl, whisk together the confectioners’ sugar, cocoa powder, cornstarch and salt. Stir in the egg whites until the mixture is smooth then stir in the chocolate chips.
Drop tablespoons of dough, 2 inches apart, onto the prepared baking sheet.
Bake the cookies for 12 to 15 minutes until the tops are set and crackly. Remove the cookies from the oven and immediately sprinkle them with the sea salt. Transfer the cookies to a rack to cool completely.
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