Using a heavy pot, heat the oil on medium-high and sauté the onion, jalapeño, and dry ingredients for 2 to 3 minutes, until the onion is translucent.
Add the broth and heat 3 to 4 minutes, allowing the sauce to thicken, then add the cheese and tomatoes.
Carefully simmer the queso on low heat for 3 to 5 minutes, adjusting its thickness to suit your taste by adding broth or cheese.
Serve hot and keep warm, stirring every so often to avoid the dreaded “cheese skin.”