Martha's recipe is adapted from one in Mexican food expert and chef Rick Bayless's book "Authentic Mexican."
The night before serving, pulverize the rice in a spice grinder. Transfer to a large bowl and add the almonds and cinnamon stick. Stir in 2 1/2 cups hot tap water, cover, and let stand for at least 6 hours.
Remove cinnamon stick and discard. Puree the mixture in a blender until no longer gritty, about 4 minutes. Add 2 cups water and blend for a few seconds more. Set a large sieve lined with 3 layers of dampened cheesecloth over a medium bowl. Pour the almond rice mixture in, a little at time, stirring gently to help the liquid pass through, and then gather up the corners of the cheesecloth and squeeze out all the liquid. Stir sugar and salt into the strained liquid. If the consistency is too thick, add water. Cover and refrigerate. Stir before pouring into glasses.