In a pot off the heat, whisk together the cornstarch and evaporated milk. Cook over medium heat, whisking constantly and scraping the bottom and sides of the pot until the mixture thickens, about 5 minutes. Remove from the heat.
Using a wooden spoon, stir in the cheese and peppers until the cheese is melted and the sauce is creamy and smooth.
Chipotle peppers are jalapeño peppers that have been ripened, dried and smoked. They can be found in many grocery stores in the Mexican products section. If unavailable, seed and finely chop 1 small jalapeño pepper.