Melt the chocolate chips in a microwave on high for 1 to 2 minutes or until smooth, stopping to stir every 35 seconds. Set aside to cool slightly.
Using an electric mixer, beat the egg whites and vanilla extract in a large bowl to soft peaks, about 2-3 minutes.
Gradually add the melted chocolate and beat for a minute.
In a bowl, mix together the flour, cornstarch, cocoa powder, 1/2 cup powdered sugar and salt. Gradually add the flour mixture to the egg mixture and beat until to form a stiff dough, about 1 minute.
Preheat the oven to 350 degrees F and line two baking sheets with parchment paper. Place 1/4 cup powdered sugar in a wide bowl. Using a teaspoon get clumps of the dough and roll them into 1 1/2-inch sized balls using your hands. Roll them in the powdered sugar.
Place them on the prepared baking sheets (I flatten them slightly, but forgot to take a photo of that step!).
Bake for 10-12 minutes. Remove from the oven and allow to cool 1-2 minutes on the sheets before transferring to a wire rack to cool completely.
Store in an airtight container at room temperature.