Chop or tear the deli-sliced American cheese into smaller strips or squares to help it melt more quickly.
In a medium saucepan over low heat, add the milk or half-and-half and gently heat until just warm, but not simmering.
Gradually add the chopped American cheese to the pan, stirring constantly until it melts into the milk without separating or clumping.
Add the chopped green chiles or jalapeños, cumin, and chipotle powder if desired. Continue stirring until the mixture thickens into a smooth, creamy sauce.
When the queso is fully smooth and heated through (about 8 to 10 minutes), taste and adjust the seasoning if necessary.
Serve immediately with warm tortilla chips, keeping the queso warm in a slow cooker or over low flame if needed.
