Grind rice until finely ground (which I did with my Magic Bullet). Add almonds and a cinnamon stick, and cover with 3.5 cups water. Soak overnight.
The next day, pour the mixture into a blender and add sugar and vanilla. I was supposed to add more water, but my blender only holds 6 cups. I blended what I had, strained some of it through a mesh strainer, returned the solids to the blender, and added the rest of my water. I blended again, and strained all of the liquid this time.