Line two baking sheets with parchment paper or silicone baking mats. Preheat the oven to 350 degrees.
Melt the chocolate chips in the microwave for about 45 seconds and stir until smooth and glossy. Let cool for 5-10 minutes.
Beat the egg whites with an electric mixer until stiff peaks form. Beat in the vanilla.
In a mixing bowl, combine 2 cups powdered sugar, cocoa powder, and salt. Whisk well. With the mixer on low, gradually add the powdered sugar mixture to the egg whites. Beat until fully combined, scraping down the sides of the bowl as needed. Add the melted chocolate and beat until incorporated. You should have a sticky dough.
Put the remaining powdered sugar in a plate or shallow bowl. Roll tablespoons of the dough into balls and roll well in the powdered sugar. Place on the prepared baking sheets, about 2 inches apart. Bake for 10 minutes.