Put shredded pepper jack and shredded cheddar in a mixing bowl and toss with the cornstarch.
Add the can of tomatoes and chiles, the evaporated milk, the American cheese, and salt. Toss to combine.
Turn the mixture into a cast iron skillet or baking dish of your choice. Bake for 20 minutes, or until completely melted and hot throughout. Give it a stir at the 10 minute mark, and again when you take it out of the oven.
Serve asap with garnishes and corn chips.
Notes
You might be tempted to try some of the more common Mexican cheeses in this dip, but queso fresco, queso blanco, and cotija do not melt well, so avoid them.
If you want a good Mexican melting cheese, try queso asadero or queso chihuahua.
I avoid using mozzarella in queso because it creates a stringy texture we don't want.
Queso can be used as a sauce in addition to being a dip for chips. Pour it over burritos, enchiladas, or tacos. We love it over a hot plate of fries!