Here's the minimum dishes version: just pour yourself a cup of milk. Then pour almost all of that milk into a skillet. Keep about two tablespoons in the cup.
Heat up the milk on the stove. Keep stirring so it won't burn.
While the milk heats up, add the cocoa powder and mix it into the milk until you get a smooth paste. Stir in the pinch of salt and any other flavours you might want to add (see variations below).
Once the milk is as hot as you want it to be (I usually leave it just until it starts forming bubbles) pour it into your cup and mix well.
Enjoy!