Rinse the rice under cold water until the water runs clear to remove excess starch.
In a blender, combine the rinsed rice and 2 cups of water. Blend on high for about 1-2 minutes until the rice is finely ground.
Strain the rice mixture through a fine mesh sieve or cheesecloth into a large pitcher, discarding the solids.
Add the remaining 2 cups of water, coconut milk, sweetened condensed milk, vanilla extract, and ground cinnamon to the pitcher. Stir well until all ingredients are fully incorporated.
Taste the horchata and adjust the sweetness or cinnamon as desired.
Refrigerate the horchata for at least 2 hours to chill and allow the flavors to meld.
Serve over ice cubes in tall glasses, and garnish with a sprinkle of toasted coconut flakes on top.