Dark, bittersweet hot chocolate--made with water, not milk--is enjoyed in Mexico City as an alternative to coffee. It's prepared with a special Mexican chocolate that usually contains cinnamon, ground almonds and vanilla. Look for high-quality brands, such as Taza, Hernán, Rancho Gordo or Seasons of My Heart, which are sold in hockey puck-size disks. To create the classic foam, you can use a blender, a whisk or a wooden instrument called a molinillo and a tall, heatproof pitcher, such as a chocolatera. Both are available online.