This frozen chocolate drink is synonymous with the Serendipity 3; the little café in New York City where people like Jackie Kennedy had their own tables.
In a medium saucepan over medium heat bring the milk to a simmer. Add the semi-sweet chocolate, hot chocolate mix, granulated sugar, and table salt, whisking, until the chocolate has completely melted.
Remove the pot from heat and let the mixture cool to room temperature. To quickly cool the mixture create an ice bath by adding the hot chocolate to a small mixing bowl. Fill a larger mixing bowl part-way with ice water and set the smaller bowl inside the ice water until cooled to room temperature.
Add the cooled chocolate mixture and 3 cups of ice to a blender and blend until completely combined, adding a bit more milk if the mixture is too thick.
Pour the mixture into a large glass or mug and top with whipped cream and chocolate shavings. Serve with straws and spoons.