Whisk together powdered sugar, cocoa powder, cornstarch, and kosher salt in a large mixing bowl until no lumps remain.

Gently add egg whites and vanilla extract to the dry mixture, stirring until a shiny, thick dough forms.

Fold in semi-sweet chocolate chips until evenly distributed. Cover and chill in the fridge for 1 hour.

Preheat oven to 350°F (175°C), line baking sheets with parchment paper, and lightly spray with cooking spray.

Divide chilled dough into 12 portions, rolling into balls spaced 2 inches apart on the baking sheets.

Bake cookies for 12-16 minutes until tops are cracked and shiny, while centers remain soft.

Cool cookies on baking sheets for at least 1 hour before enjoying or storing.