Soak the beans (night before): Rinse 2 cups dried pinto beans in a large bowl and drain. Cover with fresh water so the beans are submerged by about 2 inches; let sit on the counter overnight.
Drain and prep: The next day, drain the soaking water and set the beans aside.
Preheat the Instant Pot: Plug in the Instant Pot and select Sauté; press the + button until it reads More for high heat. Wait until the display says Hot.
Build the flavor base: Add 1 tablespoon avocado oil, 1 cup white onion, 1 Serrano pepper, 1/2 cup cilantro stems, and 2 teaspoon ground cumin. Sauté about 7 minutes, until the onions begin to soften. Press Cancel.
Pressure cook the beans: Add the 2 cups soaked pinto beans, 2 cups homemade chicken stock, and 2 teaspoon salt; stir to combine. Secure the lid and set the valve to Sealing. Select Manual (High Pressure) and set the timer for 11 minutes.
Natural release: When the timer finishes, unplug the Instant Pot and allow the pressure to release naturally; wait until the float valve drops before opening the lid.
Blend until creamy: Use an immersion blender to blend the beans until smooth and creamy. If they seem too loose, let them sit uncovered a few minutes to steam off moisture, then blend again to your desired consistency.
Alternative blending option: If you don’t have an immersion blender, carefully transfer the beans to a blender or food processor and blend until smooth.
Serve: Transfer to a bowl and serve warm.