Preheat oven to 400°F (204°C). Spray 2 large baking sheets with nonstick spray.
Melt 1 cup of chocolate chips in a glass bowl in the microwave, stirring 3 times, for about 2 minutes overall. Cool slightly.
Using an electric mixer, beat whites (3) in a large bowl to soft peaks. Gradually beat in 1 cup sugar. Continue beating until the mixture resembles a meringue or soft marshmallow creme.
Whisk 1 cup sugar, cocoa (1/2 cup), cornstarch (1 tablespoon with 3 tablespoons cold water), and salt (1/4 teaspoon) in a medium bowl to blend.
On low speed, beat sugar (1 cup) + cocoa mixture ingredients into meringue. Stir in lukewarm chocolate and 1/2 cup of chocolate chips (the dough will become very stiff).
Place 1/2 cup powdered sugar in a bowl.
Parse out the dough using a medium cookie scoop with the dough leveled off at the top of the scoop. Roll dough into balls; roll in powdered 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 the rack for 10 minutes. Transfer to cooling rack.