First, wash and drain your rice. Add it to a large bowl with the cinnamon sticks and 4 cups of boiling water. Let the water cool to room temperature, then cover the bowl and transfer it to your fridge for at least 5-6 hours, but preferably overnight.
Add your almond milk and cane sugar to a small saucepan. Bring it to a low boil, then reduce heat and simmer for 20-30 minutes, or until the liquid is reduced by about half. Let it cool, then cover and store it in your fridge until you are ready to use it.
When the rice is ready, remove both cinnamon sticks. Add the rice and water to your blender and mix on medium until smooth, about 3-5 minutes. You may have to blend in 2 separate batches depending on the size of your blender.
Note: you have a few options for blending the cinnamon. You can blend the whole cinnamon sticks with the rice and strain the pieces out, add in ½ tsp of powdered cinnamon, or leave both out. It all depends on your personal preference!
Once smooth, pour the rice mixture in batches through a very fine mesh strainer or cheesecloth into a large bowl. Squeeze or press down with a spoon to pass as much liquid through as you can.
Pour it through the strainer or cheesecloth at least once or twice more (to catch any extra grainy bits). Continue this process until all the rice water has been transferred to your bowl.
Mix in the rest of the water, reduced almond milk, and vanilla. Taste and adjust the sweetener if you want. If you prefer a thinner consistency, add in more water. If you prefer it creamier, add in fresh almond milk.
Transfer to a large jar or pitcher for storage. Serve your horchata chilled on ice with a sprinkle of cinnamon on top. Enjoy!