I blend together 3 cups skim milk (only type I had), 1/4 cup cocoa powder, 3/4 cup powdered sugar, salt, and 3 eggs until it is completely homogenized. I use powdered sugar because it blends easier and the cornstarch in it will help thicken the mixture. Then I put this in a pot over medium heat until it is very hot, but not boiling (boiling could both curdle the milk and eggs + mess up the ratio). Make sure that you continue to blend the mixture while it is heating - it should start to foam.
Next, strain the mixture and put it into an iSi Creative Whip and charge it with nitrous oxide. Give it a very good shake and serve immediately.
If you do not use up all of the hot milkshake just put it in the fridge for the next day and you will have a cold milkshake.