In a large saucepan, heat the butter over medium heat. When the butter is melted add the diced onion and jalapeno to the saucepan and cook until soft, about 4 minutes. Stir in garlic and cook for one more minute or until fragrant.
Add the cream cheese and 1 cup of the milk and stir until melted and smooth, this will take about 3-4 minutes, on low-medium heat. Stir in salt, pepper, onion powder and cumin.
Turn to the heat to LOW and add the shredded cheese, ½ cup at a time, stirring constantly. You do not want this mixture to boil, you want it to melt slowly or you will get a grainy cheese sauce.
When the cheese is melted add the remaining ¼ cup of milk, stirring constantly while you add it.
Remove the pan from heat and stir in green chiles, tomato and cilantro.
Pour the queso into a serving bowl, garnish if desired and serve immediately with tortilla chips.