Preheat oven to 350 degrees F. Line two baking sheets with parchment paper or Silpat (you’ll want to do this as the dough and cookies are very sticky and this makes for easy cleanup).

In a large mixing bowl, sift together powdered sugar, cocoa powder, cornstarch and salt and then whisk until well blended.

Add in egg whites, egg and vanilla extract and mix until well combined. Fold in chocolate chips.

Drop dough by the heaping tablespoonfuls onto prepared baking sheets, spacing cookies 2-inches apart. Bake in preheated oven until cookies are puffed and crackled, about 14 minutes, rotating sheets to opposite rack once during baking (I baked one sheet at a time and kept it on the middle rack).

Remove from oven and sprinkle tops lightly with sea salt if desired. Allow to cool on baking sheet 5 – 10 minutes then cool on a wire rack. Store in an airtight container at room temperature.