Preheat oven to 120 degrees C. Line two baking trays with baking paper, and set aside.
In large metal or glass bowl, beat the egg whites on high speed with an electric mixer until soft peaks form. Gradually add sugar while continuing to beat until they hold stiff peaks. Mix in the vanilla and cocoa on low speed, then fold in chocolate chips by hand. Drop small mounds of the mixture onto the prepared baking trays, spacing 2cm apart.
Bake for 1 hour in the preheated oven. Turn off oven, and leave the drops in the oven for two more hours, or until centres are dry. Remove from tray and store in an airtight container.