Dissolve the cornstarch in 1 cup of milk.
Set aside until ready to use.
In a stockpot, add the remaining milk, Mexican chocolate, and cinnamon stick.
When the chocolate is completely dissolved, add the sugar and the cornstarch milk.
Stir to combine.
Bring to simmer, stirring occasionally.
Once your atole has thickened, it is ready to serve.
Serve immediately to avoid lumps.