In the pitcher of your blender, combine rice, 2 cups water, and ground cinnamon. Pulse just until the rice is broken up into smaller chunks. Place the blender pitcher covered in the refrigerator for several hours, preferably overnight.

Add 2 cups of water and sweetened condensed milk to the blender. Blend on high until as smooth as possible. Using a fine mesh strainer, strain the horchata into a pitcher.

In a cocktail shaker, combine horchata, Rumchata, and silver tequila. Shake with ice and strain into a glass rimmed with cinnamon sugar and filled with ice.