Preheat oven to 350 degrees. In a large bowl, whisk together powdered sugar, cocoa powder, cornstarch, and salt until well-blended.

Separate 2 of the eggs, saving whites in a bowl and discarding yolks. Whisk egg whites.

Add remaining egg to egg whites. Whisk well..

Add vanilla to egg mixture. Whisk well.

Add egg mixture to dry ingredients. Mix until blended. The dough should be fairly stiff and seem hard to mix–the eggs will not seem to mix with the dry ingredients at first. Keep mixing. If the dough seems too runny, add a little more powdered sugar and cocoa powder.

Add chocolate chips to dough; mix until blended.

Drop spoonfuls of cookie dough onto 2 cookie sheets lined with parchment paper. Bake at 350 degrees for 12-14 minutes, rotating cookie sheets once during baking.

Remove cookies from oven. Let cool for a few minutes on cookie sheet, then cool completely on wire rack. Makes approximately 2 dozen cookies. (110 calories apiece)