Chef John's Horchata
You can substitute 1 1/2 teaspoons ground cinnamon for the cinnamon stick.
Depending on your tastes, you can alter the amount of sugar, as well as the ratio between rice and almonds, but what you can't alter is the need to strain this before serving. Unless you like gritty drinks, you'll want to pass this through a very, very five sieve, multiple layers of cheesecloth, or both.
Once blended, let sit overnight before straining, if possible. This way the water has plenty of time to leach out the goodness from the rice and almonds. The four-hour method does work, but you don't get quite the same flavor. Along the same lines, many horchata "experts" actually prefer to not blend immediately, but rather let the mixture sit overnight to soften, before blending the next day. If you like how this comes out, feel free to experiment, and test for yourself.