sockittome123 if the chocolate goes grainy it means its seized, supposedly that happens if it comes into contact with water when you're heating it (I always thought it was if you heated it too quick but just googled and supposedly its water).
My favourite way to make hot chocolate is melt a dairy milk into full fat milk - whipped cream and marshmallows on top. Amazing. Will try adding double cream next time I make it, for extra creaminess. I had a great hot chocolate at Edinburgh zoo where they put the marshmallows underneath the cream so that they melted and it was lovely.