1 cup cheese (Monterey jack, Asadero or Chihuahua), finely shredded
4 ounces green chiles
1/4 cup half-and-half
2 tablespoons finely chopped onion
2 teaspoons ground cumin
1/2 teaspoon salt
1 serrano or jalapeno pepper, finely chopped (optional)
1 tablespoon finely chopped fresh cilantro (optional)

Put all ingredients in a double boiler and cook over medium or medium-low heat until melted and well blended, stirring occasionally. Serve with fresh tostadas or hot flour tortillas