Remove skins from raw almonds as follows: Bring a medium pot of water to a boil and add the raw almonds. Blanch for approximately 1 minute. Drain the almonds under cold water. Remove the skins of the almonds by squeezing the fat end of the nut – the nut should slip right out of the skins. Dry with a paper towel.
In a dry skillet toast the dry, skinned almonds over medium heat until lightly brown. Remove from heat and allow to cool.
While the nuts are cooling, heat 3 cups of water to boiling temperature.
In an electric spice grinder, pulverize the rice into a very fine powder.
Combine the pulverized rice, toasted almonds, and the cinnamon stick into a large bowl. Pour in the 3 cups of hot water and stir to break up any clumps of rice that may form. Cool to room temperature. Cover and allow to stand overnight at room temperature.
While rice mixture is sitting, you can prepare the Concentrated Simple Syrup by heating the ¼ cup of water and the ½ cup granulated sugar in a small saucepan, stirring until the sugar completely dissolves. Cool, then chill the syrup for later.
The next day, pour the rice mixture (including the almonds and the cinnamon stick) into a blender. Add the remaining 2 cups of water and blend very well – until the rice, almonds and cinnamon stick are completely combined and pulverized.
Strain the mixture into a bowl or pitcher – you will want to strain out as much of the sediment as possible so line a mesh strainer with 3 layers of cheesecloth and pour the blended mixture through to drain into the bowl. (Alternately, you can use one of these nut milk bags to strain your horchata.)
Once drained, stir in the chilled simple syrup. Chill until cold.
When ready to serve, pour over ice and garnish with a sprinkle of cinnamon.