Add halved onion and serrano pepper pieces, garlic cloves, and bay leaf. Cook and stir for a couple of minutes.
Add bouillon, beans, and water. Set Instant Pot to "Beans/Chili" and cook for 30 minutes and let the steam naturally release (about another 15-20 minutes). If using a regular pot, cook for about an hour and a half or until the beans become soft and tender. Soaking the beans beforehand will reduce the cooking time.
Remove bay leaf, onion and serrano pieces. Mash up any remaining chunks of garlic. Season and serve!