You will need a Braunstyle hand blender.
Brew a pot of robust French Roast or Espresso style coffee. In a small sauce pan warm whole milk and add cocoa. Pour two large coffee cups 3/4 full. While milk is coming to a simmer use hand mixer on high speed to create froth and incorporate the cocoa. Once the "chocolate milk" has a nice foamy head, carefully pour milk into coffee cup spooning foam on top.
Dust with cocoa