Finely chop the chocolate and set aside.

Pour the milk and espresso into a small saucepan. While still cold, sift in the cocoa powder and cornstarch and whisk until smooth.

Add the sugar and bring the mixture to a slight boil over medium heat, stirring until the sugar is fully dissolved.

While continuously whisking, add the chopped chocolate and continue cooking until the mixture is smooth, creamy and has thickened (about 5-7 minutes).

Top with whipped cream and sprinkle with cinnamon if desired.