In a 2- to 3 quart saucepan, stir the milk, water and sugar together.
Add a little more sugar.
Bring to a boil over medium heat.
Whisk in the chocolate and cocoa powder.
Keep whisking over the heat until the solids have dissolved and then thickened.
Reduce the heat to very low.
Using an immersion blender whirl at high speed for 1/2 a minute or more, until the hot chocolate is thick and foamy. (You may want to tilt the immersion blender to incorporate more air, taking care not to get ho t chocolate all over everything.) Alternatively you may use a standard blender.