Heat oven to 300F; cover baking sheet with parchment paper
Beat egg whites and cream of tartar until soft peaks form; slowly add sugar, followed by vanilla; beat until stiff peaks form; sugar should be dissolved and egg whites look glossy
Sift cocoa powder into egg whites and fold gently until combined
Fold in chocolate chips, then drop even-sized scoops onto cookie sheet
Bake 35-40 minutes until cookies are just dry; cool slightly before removing from cookie sheet; transfer to wire rack to finish cooling
