Chocolat Chaud Steingarten (adapted from Pierre Hermé).
In a 2-quart saucepan, stir together the milk, water, and sugar. Bring to a boil over medium heat. Add the chopped chocolate and the cocoa and bring to a boil again, whisking until the chocolate and cocoa are dissolved and the mixture has thickened. Reduce the heat to very low.
Blend for 5 minutes with an immersion mixer or whirl the hot chocolate in a standard blender for half a minute, until thick and foamy.
Note: I use a dark chocolate containing close to 70 percent cocoa, though Lindt bittersweet also works just fine. The Mayans and the Aztecs considered the froth the best part. Today, five minutes with an immersion mixer or a blender accomplishes what a half hour of beating did long ago.