Dissolve the cornstarch in the water until there are no lumps. Set aside.
Puree the corn kernels with 1 cup of the milk in a blender until smooth.
Strain the puree through a colander or sieve to remove the corn skins, keeping the liquid.
Pour the strained corn liquid and the remaining milk into a pot with the cinnamon and sugar; heat gently, stirring.
Add the cornstarch slurry, stirring without stopping. Cook until thickened - the source notes this stage can take 15 minutes or more before the drink reaches full body.