Melt the butter in a saucepan over medium-low heat, then add the poblano and jalapeño.
Cook the peppers for about 3 minutes, add the garlic, and continue cooking for another 30 seconds.
Sprinkle in the flour and whisk continuously for approximately 1 minute to remove its raw flavor.
Slowly pour in the milk while whisking, then cook until the mixture begins to thicken.
Reduce the heat and add both cheeses gradually, whisking after each addition until completely melted.
Stir in the cumin, salt, and pepper, then serve warm or thin with extra milk if needed.
