Rinse the rice under cold water until the water runs clear.
In a bowl, combine the rinsed rice, almonds, and cinnamon stick.
Add 4 cups of water to the bowl and let it soak for at least 4 hours or overnight.
After soaking, drain the mixture and discard the water.
Blend the soaked rice, almonds, and cinnamon with 2 cups of fresh water until smooth.
Strain the mixture through a fine mesh sieve or cheesecloth into a pitcher.
Add the remaining 2 cups of milk (or almond milk) to the strained mixture.
Stir in sugar and vanilla extract, adjusting sweetness to taste.
Chill in the refrigerator for at least 1 hour before serving.
Serve over ice with a sprinkle of ground cinnamon on top.