It's not hot chocolate. Hot chocolate is made from milk, sugar, and cocoa powder, which, while potentially very good, is produced by separating most of the fat from the cocoa solids. Drinking chocolate is made from solid chocolate, with all the fat still present to create a luscious, thick texture. Complemented by heavy cream or half and half, fine dark chocolate becomes a heavenly beverage as smooth and silky as it is rich in flavor and depth. Since it is much richer, it is often served in small quantities - just an espresso cup. Dark chocolate is classic - 65-75% works well. No reason you can't use dark milk, milk, or very high cocoa percentage chocolates either. Some inclusion bars also make for an interesting cup. Just be sure to use something good because poor chocolate quality generally becomes very apparent in drinking chocolate. The caveat to that is that sometimes bars that are a bit bland but not bad per se make great drinking chocolates, while the nuances of truly exceptional bars can be lost under the cream. If you have something that is mellow but not thrilling, give it a try.
It's very simple:
For two servings, heat 1/2 cup heavy cream just to boiling and remove from heat. The microwave is often the easiest because it's a small quantity.
Stir in 4 tablespoons of chopped or broken up chocolate. Let it sit for a moment for the chocolate to melt, then whisk until smooth. The little electric milk frothers work great. Taste and add more chocolate if desired, then pour into tiny cups and serve.
Try to avoid reheating, because weird things happen with the flavor and texture when chocolate gets cooked. The idea with the hot cream is that you can just melt the chocolate without heating it directly. If needed, microwave it for just 10 seconds or so or heat very briefly on the stovetop.
Chocolate recommendations for drinking chocolate: Mellow, nutty chocolates, such as Venezuela, work well. Felchlin's Maracaibo disks are excellent. For a very dark drinking chocolate, Original Beans' Mexico Zoque is wonderful. Spiced bars like Pacari's Chili bar are also good.