Press the Sauté button on the Instant Pot and the Adjust- button once. Add
the butter to the pot and melt completely. Add in the diced onion and a pinch of
salt and stir well. Cook for 3 minutes, stirring frequently, until the onions
are very fragrant and translucent at the edges. Stir in the garlic and cook for
Add in the green chiles and stir well. Cook for 3 minutes, stirring
frequently. Sprinkle the chili powder and cumin over the mixture, stir in, and
cook for another 30 seconds. Evenly scatter the flour over the chile and onions,
stir to make a uniform paste, and cook for 2 minutes, stirring frequently. Don’t
fret if a little of it sticks to the bottom of the pan. You just want to avoid
Pour in half of the milk and stir vigorously, scraping the bottom of the pan,
until smooth and thick, then whisk in the remaining milk. Press the Adjust +
button twice and bring the mixture to a boil, stirring or whisking constantly as
it thickens. Stir in the cheeses, all at once, and press the “Stop” button to
shut off the heat. Cover the pot and let stand undisturbed for 3 minutes.
Remove the lid and whisk until smooth and even. Adjust with salt and pepper
to taste. Let stand for 3 to 5 minutes before serving.
If desired, serve garnished with chopped fresh cilantro or green onions.