This is so simple but astonishingly delicious. It is just chocolate and milk. The secret to making a creamy, rich, frothy chocolate drink is all in the technique. You just heat it, whisk it, heat it, whisk it etc until it's the thickness you want. And it can get VERY thick. In Spain, this is often breakfast, along with churros. Traditionally, a wooden hand mill called a molinillo was used to whisk it, but a wire whisk or hand held electic whisk works just as well.