Where are the horchata experts? 
Here was my first attempt a couple of years ago. I made it to use it in a cocktail (of course) and the recipe was from PDT.
Highlights of the recipe:
The rice ("uncooked white long-grain) is ground with the water in a blender
The mixture is left to stand for 12 hours at room temperature
The mixture is strained (it doesn't say how, but I used a metal strainer lined with a nylon cheesecloth)
Milk, vanilla extract, cinnamon, and sugar are added and the mixture is blended again
Ratios
4:1 water to milk ratio (40 ounces water and 10 oz whole milk)
6:1 liquid to rice ratio (by weight) (8 oz rice)
25 g/L sugar (3 tablespoons of sugar for 50 ounces of liquid)
I remember not being too crazy about the texture which was on the chalky side, and overall it was a bit lacking in flavor. It tasted a bit thin and wasn't very sweet.
