Whisk icing sugar and cocoa powder in a bowl. Add the egg whites and vanilla essence and mix well until mixture is evenly combined.

Line trays with baking paper and place tablespoon fulls of mixture on the tray. Cookies will spread to approximately double in size so leave enough room between each cookie.

Preheat oven to 170 degrees and bake for approximately 8-10 minutes. Allow coolies to cool completely on trays before removing (otherwise they will stick to the baking paper).