Heat evaporated milk over medium-high heat in a small saucepan. Stir in the cornstarch and whisk to combine.
12 ounces evaporated milk,1 tablespoon cornstarch

Once simmering (bring it to just before boil–when it starts bubbling up the sides, it's ready), immediately reduce heat to low.

Immediately stir in the cheese in batches, starting with the white american cheese. As you stir in the cheese, increase heat to medium/low and whisk CONSTANTLY while the cheese melts. Once each batch is melted and creamy, add more. Don't stop stirring–you have to whisk the entire time while adding cheese.
3/4 lb white american cheese

Once done with the white American cheese, add in the shredded Mozzarella. Again, whisk CONSTANTLY while the cheese melts, insuring you have a creamy blend. If you prefer the cheese a bit thicker, add a bit more Mozzarella.
4 ounces mozzarella cheese

Once all the cheese is melted, stir in the jalapenos, chili powder, nutmeg, red pepper, and salt and pepper. *** (see note)
2 tablespoons canned jalapenos,1 teaspoon chili powder,1/2 teaspoon ground nutmeg,1 teaspoon red pepper flakes,1/4 teaspoon salt,1/4 teaspoon black pepper

(Optional) If you want the queso to be a bit browned (as pictured), pour the queso into a skillet and place in the oven. Broil for 3-4 minutes, or until cheese begins to bubble and brown.

Top with cilantro, tomatoes, and more jalapenos if desired.
chopped cilantro