1. Get a large bowl full of ice cold water.
2. Stir together 1/4 of the milk and the cornstarch in a measuring cup and let it sit while you whisk together sugar, cocao and remaining milk in a saucepan over medium heat. Bring to a boil while continuing to stir and add in coffee granules.
3. Add the cornstarch/milk mixure to the saucepan and bring to a boil again. Immediately remove from heat.
4. Stir the mixture and add vanilla and half of the chocolate - keep whisking!
5. Place saucepan in that bowl of ice water and whisk away! Place the mocha mixture in a container and put in fridge overnight.
6. The next day, make your icecream according to your icecream maker’s instructions. Add the remaining chocolate pieces about 5 minutes before the mixture is done churning.