Using a thick, heavy spot, heat the oil and sauté the onion and the dry ingredients for 2 to 3 minutes, until the onion is translucent.
Add the water or broth, and heat 3 to 4 minutes, allowing the sauce to thicken, then add the shredded cheese and tomatoes.
Carefully simmer the queso on low heat for 3 to 5 minutes, adjusting its thickness to suit your taste by adding water or cheese. Serve hot with salted fried flour or corn tortillas.
Servings: