Most people don't know how to make hot chocolate from cocoa properly. While if you are making hot chocolate from hot chocolate powder, you can just slop it into a mug with some milk and microwave it, this approach will not work for cocoa, or for cold chocolate. to do things properly;

  1. Put 1 heaped tablespoon of cooking cocoa, and 2 table spoons of caster sugar into a pint glass, or big-ass mug.
  2. Add a few drops of full-cream milk, and stir with a spoon until it forms a lump of chocolate. If it has a liquid consistency, you added too much.
  3. Add about twice as much milk again, and mix to a thick paste
  4. Continue stirring, and add progressively more milk, rather like making mayonnaise, until you have a full pint glass.
  5. Nuke for 2 minutes or so, or drink with ice, depending on the season
If you just arbitrarily mix the ingredients, the cocoa, which is abjectly hydrophobic, will not go into suspension in the milk, and you'll end up with an undrinkable mess.