Restaurant-Style Queso Blanco

cooking oil (veggie, olive, canola - whatever you have)

white onion, diced

large jalapeno or serrano, seeds and stem removed; diced

white American cheese (I have the deli give me 3 slices on 10), shredded

Monterrey Jack cheese, shredded (optional; don't use pre-shredded)

cream, half-and-half, or whole milk

roma tomatoes, seeds removed and diced

small bunch cilantro, roughly chopped