In a medium sized bowl combine rice and water. Split cinnamon sticks in half to expose cinnamon flavoring, and add to rice water. Cover and place in refrigerator overnight, or for at least 8 hours.
Remove from refrigerator, and remove all large pieces of cinnamon sticks.
Pour rice and water into a blender that holds at least 6 cups or 48 ounces of liquid. Blend on high for 2-3 minutes, or until rice is finely blended.
Using a fine mesh strainer or cheesecloth, strain rice milk into a pitcher leaving the ground up blended rice. Use a spatula or back of a spoon to press, getting all excess rice milk out of rice. Discard ground rice.
Add sugar and milk to cinnamon rice milk mixture. Whisk until well combined. Chill in refrigerator for 30-45 minutes prior to serving.
Serve chilled over ice. May garnish with a dash of ground cinnamon.
The more traditional recipe of horchata would omit added cows or coconut milk, and it would purely be a rice milk drink. To do this simply add 2 cups cold water in place of the milk called for when adding granulated sugar.