Using electric mixer, beat whites in large bowl to soft peaks. Gradually beat in ½ cup powdered sugar. Continue beating until mixture resembles soft marshmallow creme.
Whisk 1 cup powdered sugar, cocoa, cornstarch, and salt in separate bowl. On low speed, beat the dry ingredients into the egg white meringue. Once it is fully incorporated, add the lukewarm chocolate and ½ cup chocolate chips. Dough will become very stiff. If your dough seems loose at all, I recommend refrigerating the dough for at least a half hour to help it firm up before rolling into balls.
Place ½ cup powdered sugar in bowl. Roll 1 rounded tablespoon of dough into a ball and roll in powdered sugar. Place on baking prepared sheet. Repeat with remaining dough, spacing the cookies 2 inches apart.
Cornstarch can be replaced with tapioca or arrowroot starch to keep it grain-free.