Preheat oven to 350 degrees F. Line 2 cookie sheets with parchment paper; lightly coat with nonstick cooking spray. In large bowl, whisk confectioners' sugar, cocoa, and salt. Add egg whites and vanilla and beat with wooden spoon until smooth. Fold in chocolate chips. Set dough aside 5 minutes. If your batter is too runny, cover and refrigerate 10 minutes or until slightly thickened. Drop dough by rounded tablespoonfuls, 2 inches apart, onto prepared cookie sheet. Bake 13 to 15 minutes, or until set and crackly. Let cool on cookie sheets 3 minutes; then, with spatula, carefully transfer to wire racks to cool completely.