Pour the milk into a wide skillet and bring to a boil. Reduce to a simmer and cook, stirring frequently, until reduced by half, 2030 minutes. Strain into a large saucepan and add the water and cinnamon sticks.
Bring to a boil, reduce to a simmer and cook 5 minutes. Remove from the heat and let sit 15 minutes. Remove the cinnamon sticks and reserve.
Combine the rice flour, sugar and vanilla in a bowl. Pour in the milk mixture and whisk to incorporate well. Refrigerate at least 4 hours. Then pour the liquid into a pitcher, discarding the sediment that has settled on the bottom of the bowl. Serve cold over ice, with cinnamon sticks as stirrers.
c.1997, M.S. Milliken & S. Feniger, all rights reserved