Pour 4 cups of milk and 1½ cups dry, uncooked rice in a blender.

Add ¼ cup sugar, ½ teaspoon ground cinnamon, and ½ teaspoon vanilla, then blend for 1 minute.

Strain the liquid in a fine mesh strainer over a large pitcher.

Place the rice back into the blender and add an additional 4 cups of milk along with ¼ cup sugar and ½ teaspoon each of ground cinnamon and vanilla; repeat this process two additional times with the remaining milk.

Combine all the milk mixture into a large pitcher or place back into the gallon milk container and stir to combine.

Let sit in the fridge for as long as you can, up to 48 hours (10 minutes will do too, if you don't have time).

When you are ready to serve, stir the horchata and then pour over ice.