Place the rice in a heatproof bowl or jar and add the boiled water. Stir and set aside to cool to room temperature. The rice will soften slightly.

Transfer the rice and soaking water to a blender and blend until the rice is finely chopped and almost dissolved.

Strain the liquid into a large bowl or jar and discard any remaining bits of rice. Add the milks and cinnamon, stir well and refrigerate for 30 minutes.

Add 2 cups (500 ml) water to the horchata and stir it all together. Serve, poured over ice.