Place the chocolate drink in the jar of your blender. Whisk the milk, 1 cup cream, egg yolks, sugar, and salt in heavy medium saucepan until smooth. Cook over medium-low heat, stirring constantly, until the mixture is almost boiling and is thickened and coats the back of a spatula. 

Pour the mixture over the chocolate in the blender jar and add the vanilla. Place the lid on the blender jar and blend until smooth, stopping to scrape down the sides as necessary. Divide the mixture evenly into ramekins or small jars (it should just pour right out). Chill until set, about 2-3 hours.

Whip the remaining cup of heavy cream with 1/4 cup powdered sugar until soft peaks form. Dollop on top of the pots de creme and, if desired, garnish with shaved chocolate and serve.

Note: These can be made 2-3 days in advance and refrigerated until ready to serve; after they chill, just cover tightly with plastic wrap until ready to serve.