How can I make my Hot chocolate thicker?
Spanish hot chocolate and Italian cioccolata fiorentina both use cornstarch as a thickening agent. Both are used more for dipping or sipping (churros in the former case), however you could easily just use less cornstarch to make it more 'drinkable'. 

Try a teaspoon of cornstarch, mixed with a little cold water, added to the milk when you boil it.

As Kate Gregory suggests, you could also use full-fat milk, or loads of shaved chocolate.