Bring milk to a boil in a medium saucepan over medium-high heat.
When the milk is just boiling, lower the heat to medium and whisk in 60% dark chocolate.
When the chocolate has melted, add cornstarch and milk powder to the mixture and continue to whisk until the mixture is smooth and thick.
Divide the cocoa into mugs and garnish with whipped cream or marshmallows if you like.
