Step 1

In a large pot, add the beans, half of an onion and epazote, and cover with 14 cups of water. Set over high heat, bring to a rolling boil, cover, and reduce the heat to medium low. Cook for an hour, remove the lid to check if beans are cooked and soft. If they aren't, continue cooking for another 10 to 15 minutes and make sure there is still sufficient liquid. If not, add a couple more cups of hot water. Once the beans have completely softened, add the salt, stir, cover the pot, and cook for 5 more minutes. Turn off the heat and let cool.

Step 2

Remove the epazote and onion. In batches, using a blender or food processor, puree the beans and their liquid until completely smooth.

Step 3

In a large skillet or saute pan, heat the oil over medium heat until it shimmers. Add the chopped onion and whole chiles, and cook until the onion is translucent and begins to brown, and the chiles soften and start changing color. Add the pureed beans and continue cooking, stirring occasionally until thickened to your liking. Taste for seasoning and set aside.