Add the rice and cinnamon stick to a large bowl. Add 6 cups of water. Cover the bowl and transfer to the refrigerator to soak for 10-12 hours.

Add half of the soaked rice and water to the blender. Blend for 1 minute then strain into a pitcher using a fine mesh strainer. Then repeat with the remaining soaked rice and soaking water. Discard the solid bits that are left behind in the strainer.

Add the sweetened condensed milk, sugar and evaporated milk to the blender and blend for 15 seconds.

Strain into the pitcher using the fine mesh strainer.

Add the vanilla and remaining 4 cups of water to the pitcher. Stir well.

Serve over ice. Top with ground cinnamon if desired. Store the leftover horchata in the refrigerator.