Put rice, 3 cups water, and cinnamon sticks in blender. Blend for about 1 minute to break up the rice and cinnamon sticks.
Transfer rice water mixture to a large pitcher or allow to sit in the blender add as much of the remaining water as you can. Let mixture soak overnight, or at least 3 to 4 hours.
Strain rice mixture through a double layer of cheese cloth (or coffee filter) into another pitcher or a large liquid measuring cup.
Add the remaining water, milk, vanilla, and sugar and stir well. If desired, refrigerate until well chilled.
Serve in with ice, if desired.
Makes 2 quartsIt's best to make it a day ahead...but I will admit I never seem to remember to do it that far ahead. The longer it sits the better it tastes.If you would like a stronger cinnamon flavor, add additional cinnamon sticks to the blender when blending.You can also add 3/4 to 1 tsp of ground cinnamon to the finished drink but be aware that it doesn't mix in well and may clump slightly.I prefer to use Mexican vanilla for its richer flavor.