How to Make It
In a bowl, cover the rice with the water. Add the cinnamon sticks and let stand at room temperature for at least 3 hours or overnight; discard the cinnamon sticks.
Meanwhile, in a skillet, toast the almonds over moderate heat, tossing, until fragrant, 3 minutes. In a small bowl, blend 1 tablespoon of the ground cinnamon with the sugar.
Transfer the rice and its liquid to a blender. Add the almonds and puree for 2 minutes. Strain the horchata through a fine sieve into a bowl. Rinse out the blender.
Return the horchata to the blender and add the condensed milk, banana and the remaining 1/4 teaspoon of ground cinnamon and puree. Add the ice cream and ice and blend. Pour the shake into glasses, sprinkle the cinnamon sugar on top and serve.