vegetable oil spray
1 ½ cups bittersweet chocolate
3 large egg whites, room temperature
2 cups pure icing sugar, divided (plus ½ cup to sprinkle over cookies)
½ cup unsweetened cocoa powder
1 tablespoon cornflour
¼ teaspoon salt
Preheat oven 175°C.
Spray 2 large baking sheets with nonstick spray. Set aside.
Melt 1 cup chocolate chips in glass bowl in microwave, stirring frequently, about 2 minutes. Set aside and let cool slightly.
Using electric mixer, beat whites in large bowl to soft peaks. Gradually beat in 1 cup sugar. Continue beating until mixture resembles soft marshmallow cream.
Whisk 1 cup sugar, cocoa, cornflour, and salt in medium bowl to blend. Then, on a low speed, add these dry ingredients into the marshmallow cream mixture.
Next, add remaining ½ cup chocolate chips to lukewarm chocolate mixture (dough will become very stiff).
Add chocolate mixture to cream mixture and blend well.
Place remaining ½ cup icing 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.