Add uncooked rice, cinnamon sticks and 2 cups of water to a blender and blend for 2 minutes. Add 2 more cups of water and blend again until the cinnamon sticks and rice are finely ground.

Pour into a large pitcher or other tall container with a tight fitting lid and let soak for at least 6 hours or overnight.

Using a cheesecloth or a fine mesh strainer, strain the mixture into a large pitcher. Discard the rice.

To the pitchers, stir in sugar and milk until sugar is dissolved. Pour horchata over ice in glasses. Sprinkle cinnamon on top for garnish.