Add the beans, liquid, 1/2 of the onions, garlic, and herbs to the Instant Pot container. Close the lid and seal the vent. Set for high pressure for 40 minutes (if using an Instant Pot model with the Bean/Chili setting, use it instead and increase cooking time to 40 minutes). When cooking is complete, let pressure release naturally, about 15 minutes. (If it goes longer than that, you can finish with quick release.)

Heat 2 tablespoons of vegetable broth (or 1 tablespoon oil) in a large skillet (cast iron, or enameled cast iron recommended) over medium heat until simmering. Add the remaining onions and Hatch chilis, and saute until soft, about 8 minutes.

Drain the beans in a large sieve, reserving the cooking liquid. Add the beans to the skillet and mix thoroughly with the onions. Reduce heat to medium-low, and cook for 10 minutes.

For chunky refried beans, use a potato masher to break up the black beans to your desired consistency. Add small amounts of the cooking liquid as necessary. (Make sure you're using a skillet with a surface that can take metal tools if your masher is metal.)

For smooth and creamy, restaurant-style refried beans, transfer the contents of the skillet back to the pressure cooker pot. Add 1/4 cup of the cooking liquid, and use an immersion blender to smooth out the beans. Add more liquid, a little at a time as necessary, until the beans reach your desired consistency.

Sprinkle a 1/2 teaspoon of salt over the beans and mix well. Taste, and add more salt as needed, a pinch at a time.