Pick over the beans to check for any stones, or beans that look bad. Then rinse thoroughly.
Add the Vegetable Oil (3 tablespoon) to a deep pot over medium heat. Add the Yellow Onion (1) and cook until golden, stirring often, about 10-15 minutes.
Add Black Beans (1 pound) and Water (2 quart) to the pot with the onion. Remove any beans that float. Add Epazote (1 sprig) if using, and bring to a boil. Reduce heat and simmer, partially covered, for about 2 hours.
Stir the beans from time to time, and make sure that the water is about 1/2 inch above the beans at all times. Add more if it sinks below this level. You want the beans to be cooked all the way through and creamy. If they aren’t ready after 2 hours, simmer a little longer, adding a bit more water if necessary.
Once beans are cooked all the way through, add the Kosher Salt (1 1/2 teaspoon) and simmer for another 10-15 minutes. Serve topped with crumbled Cotija Cheese (to taste) on top, garnish with Fresh Cilantro (to taste).