Wash and drain the rice. Using a spice grinder (an electric coffee grinder works well too), grind the rice until fine; combine with the almonds and cinnamon bark. Add 3 1/2 cups water and let sit overnight, covered. Blend rice mixture until smooth using a blender. Add 2 1/2 cups of water and continue blending. Add sugar and vanilla extract. Strain horchata into a bowl first using a metal strainer and then a double layer of cheesecloth; finish with up to an additional 2 cups of water until it achieves a milky consistency. Enjoy over ice.