Preheat oven to 375°F (190°C). Line two baking sheets with parchment paper.
In a large bowl, whisk the egg whites and powdered sugar until smooth, glossy, and fully combined. The mixture should look thick and shiny.
Add cocoa powder, salt, and vanilla. Gently fold until just combined. The batter will look more like brownie batter than cookie dough.
Fold in chocolate chips.
Scoop about 2 tablespoons of batter per cookie onto the baking sheets, spacing well apart since they spread.
Bake for 2 minutes at 375°F, then reduce oven temperature to 350°F (175°C) and continue baking for 8 to 9 minutes until tops are shiny and crackly but centers are still soft.
Cool on the baking sheet for 5 minutes, then transfer to a rack to finish cooling.
Notes
If you want ultra dramatic crackles, make sure the powdered sugar is fully dissolved before adding the cocoa. Smooth batter equals shiny tops.
These cookies are best slightly underbaked. They will set as they cool, so trust the soft center.
For extra edge energy, let them cool completely. The texture gets even chewier as they rest.