Soak the rinsed rice in 2 cups of water for at least 4 hours or overnight.

Drain the rice and place it in a blender with the remaining 3 cups of water. Blend until the rice is finely ground.

Strain the mixture through a fine mesh strainer or cheesecloth into a large bowl, discarding the solids.

Add the milk, sugar, vanilla, cinnamon, and salt to the strained rice water. Stir well to combine.

Chill the horchata in the refrigerator for at least 1 hour before serving.

Serve over ice and sprinkle with additional cinnamon if desired.