Whenever I make hot cocoa for dinner guests or visiting friends, I make it the old fashioned way with whole milk and heavy cream blended with high quality chopped chocolate. It simmers on the stove-top until steamy and then it's poured into extra-large mugs. An obscene amount of whipped cream is usually the finishing touch.
Without guests to serve, I'm more likely to make myself a cup of instant hot cocoa. I'm the only one in the house who drinks it regularly, and I find it's more convenient to make (and there's no pot to clean!). I've developed a powdered formula that can be poured into a mug and roused into a satisfying treat with just the addition of hot water or hot milk.