Melt butter over medium heat in a medium saucier.
Add garlic and onions, cooking slowly for about 3 minutes or until onions are translucent.
Add diced tomatoes and cook for an additional 3 minutes or until tomatoes begin to break down/soften.
In a medium bowl, combine evaporated milk and cornstarch. Whisk until cornstarch is dissolved.
Add milk and cornstarch mixture to the saucier.
Stir until the mixture begins to thicken and then add shredded cheese. Continue to stir until cheese has completely melted.
Add cumin, salt, black pepper, green chiles, and cilantro and stir.
Bring queso to a simmer and cook for 2-3 minutes.
Serve warm topped with pico de gallo and tortilla chips.