Sort the beans, rinse them well, and place them in a large pot with 1/4 small white onion, 2 garlic cloves, 4 leaves epazote herb, 1 large jalapeño pepper, and 6 cups water; cook until the beans are tender, then add the salt and cook 10 minutes more for a total of 1.5 to 2 hours. The beans should mash easily between your fingers, and the broth will smell earthy and fragrant from the onion, garlic, and herbs.

Drain the beans and keep the cooking liquid nearby for the skillet stage. Do not discard that broth because its starch helps the beans turn creamy instead of dry.

Set a large cast iron skillet over medium heat and add 3 tablespoons olive oil. The oil should look fluid and shimmer lightly before anything else goes in.

Add 1/3 cup white onion, finely chopped, and cook until golden and a little crisp, then stir in 1 clove garlic and 2 whole chiles de arbol for 2 minutes. The onions should smell sweet and savory, and the chiles should smell toasted but not burnt.

Add the cooked beans with 1/4 cup reserved bean broth, then mash them directly in the skillet with a potato masher and stir in the large pinch sea salt. You should hear a lively sizzle at first, and the beans will start to darken slightly as they absorb the oil.

Lower the heat and cook for 8 minutes, stirring often and adding more broth as needed while continuing to mash until the texture suits you. The finished beans should look creamy and glossy and pull away from the bottom and sides of the skillet when stirred.

Spoon the beans out while they are still hot and soft. They will thicken a bit as they sit, so the skillet texture should look slightly looser than the final serving texture.