In a saucepan, melt the butter over low heat. Whisk in the flour until the mixture starts to bubble.
Pour in the half-and-half and stir until well blended. Add the garlic salt, onion powder, chili powder, and cumin.
Mix in the Monterey Jack cheese and stir until melted and smooth. Toss in the chopped cilantro and the serrano pepper. Mix well.
Serve immediately with tortilla chips. Enjoy!
To reheat the queso dip, place it in the microwave, stirring it every 30 seconds until it is creamy and hot.