Stir together 2 tablespoon of the whole milk and the cornstarch in a small bowl. Set aside.
Add the remaining milk to a small saucepan, along with the powdered sugar, milk chocolate, and cocoa powder. Whisk over low heat until everything is melted and well combined.
Slowly pour in the cornstarch mixture and whisk thoroughly. Allow to thicken over low heat for 1-2 minutes, until steaming but not simmering.
Remove from heat and divide between 2 small cups. Drink up!