Notes: Horchata is a traditional Latin beverage made from rice softened in water, with cinnamon and sugar. To finely grind the soaked rice, use a blender with sharp blades; it may take several minutes to blend each batch until smooth. You can prepare the drink through step 2 up to 1 day ahead; cover and chill.
How to Make It
In a bowl, combine rice and 10 cups water; cover and chill until grains break easily when squeezed, about 24 hours, or up to 2 days.
In a blender, whirl about 2 cups of the rice mixture with sugar, vanilla, and cinnamon until sugar is dissolved and mixture is smooth; pour into a large bowl or pitcher (at least 3 1/2 qt.). Whirl remaining rice mixture without seasonings, in batches if necessary; add to bowl and stir until well blended with flavored batch. Taste, and add more sugar if desired.
Just before serving, stir mixture (ground rice will have settled to bottom). Fill glasses with ice cubes, then horchata.