Dark chocolate laced with cinnamon and covered in coarse sugar. A Nestle product.
To make Mexican hot chocolate, break tablet of Mexican chocolate into pieces and bring it to a simmer with milk. Stir the mixture until the chocolate is melted and well-combined.
Mexican chocolate is traditionally beaten to a froth with a wooden implement called "molinillo". You can imitate the effect by putting a small amount of your chocolate at a time in a blender and briefly pulsing it.