Cribbed from Marcela.

3 tablespoons vegetable oil, divided
1/2 medium white onion, chopped
2-3 poblano chiles, stemmed, seeded and chopped
1 clove garlic, peeled and roughly chopped
1 cup chicken or vegetable broth, plus more if needed
1 cup long grain rice

Heat 2 tablespoons oil in a medium, heavy nonstick skillet over medium heat.
Add the onions and saute until translucent, about 3 minutes.
Add the poblano chiles and saute, about 8 minutes.
Mix in the garlic and cook until fragrant, about 1 minute.
Season with the salt and pepper.
Add 1 cup broth and bring to a boil.
Turn off the heat and let cool.
Transfer the mixture to a blender and process until smooth, about 1 minute.

Measure the liquid yield from the blender, adding more chicken broth if necessary to yield 2 total cups of poblano liquid.
Adjust seasoning to taste.

Meanwhile, clean the skillet, place over medium heat and add the remaining 1 tablespoon oil.
Fry the rice until slightly golden.
Pour the poblano puree into the skillet and bring to a simmer.
Turn down the heat to medium-low and cover tightly.
Cook for 30 minutes, turn off the heat and let rest for 10 minutes.
Fluff with a fork before serving.

Do Ahead
At the end of this summer's bounty poblano pepper crop, I made a mega batch of the poblano-onion-(veg)broth mixture and froze it in cubes. One cube is roughly the amount of poblano + onion for 1 cup of rice, and yields about 1/4 cup of liquid. Note that I used more concentrated broth than normal, so consider substituting some water for broth when making the rice.