How to Make It
Place cacao bean husks in a large enameled Dutch oven. Cook over medium-low, stirring often, until dark brown (not black) and fragrant, about 6 minutes. Transfer to a large plate; spread in an even layer, and let cool, about 15 minutes. Working in batches, grind husks in a spice grinder until husks become a fine powder. Transfer to a small bowl, and set aside. Wipe out Dutch oven with a paper towel.
Place masa flour in Dutch oven. Cook over medium, slowly whisking in 2 cups water. Cook, whisking constantly, until smooth. Whisk in remaining 8 1/2 cups water, and bring to a boil over medium-high, whisking bottom and sides of Dutch oven often. Whisk in cacao bean husk powder, sugar, allspice, cinnamon, and, if desired, cayenne. Reduce heat to low, and simmer, whisking often, until mixture is thickened and tastes of chocolate, about 5 minutes. Remove from heat, and whisk in vanilla. Ladle atole into warm cups, and serve warm or hot.