Combine sugar, cocoa, salt and 1 cup milk in a large saucepan or pot. Stir over medium heat until the mixture starts to boil. Cook, stirring constantly, for one full minute. Add remaining milk and heat until scalding hot (180℉ with bubbles on the side) - do not boil!
While milk mixture is heating, place the chocolate chips in a microwave safe bowl and heat in the microwave for 30 seconds. Remove, stir, and heat for another 30 seconds. Remove, stir one more time and set aside. Optional: Whip the heavy cream on medium high speed until soft peaks form and set aside.
When milk mixture reaches the scalding point, remove from the heat and immediately add the melted chocolate chips. Whisk to combine until smooth.
Serve immediately topped with a dollop of whipped cream, or switch the cream out for marshmallows for some extra sweetness.