In large bowl, beat egg whites and cream of tartar at high speed of electric mixer until soft peaks form. Gradually add sugar and vanilla, beating well after each addition until stiff peaks hold, sugar is dissolved and mixture is glossy. Sift cocoa onto egg white mixture; gently fold just until combined. Fold in chocolate chips.
Drop by heaping tablespoons onto prepared cookie sheet.
Bake 35 to 45 minute or just until dry. Cool slightly; peel paper from cookies. Store, covered, at room temperature.