1. Preheat oven to 400°F. Spray 2 large baking sheets with nonstick spray.
2. Melt 1 cup chocolate chips in glass bowl in microwave, stirring twice, about 2 minutes. Cool slightly.
3. Using electric mixer, beat whites in large bowl to soft peaks. Gradually beat in 1 cup sugar. Continue beating until mixture resembles soft marshmallow creme.
4. Whisk 1 cup sugar, cocoa, cornstarch, and salt in medium bowl to blend.
5. On low speed, beat dry ingredients into meringue. Stir in lukewarm chocolate and 1/2 cup chocolate chips (dough will become very stiff).
6. Place 1/2 cup sugar in bowl. Roll 1 rounded tablespoon dough into ball; roll in sugar, coating thickly. Place on prepared sheet. Repeat with remaining dough, spacing 2 inches apart. Bake until puffed and tops crack, about 10 minutes. Cool on sheets on rack 10 minutes. Transfer to cooling rack.