In a medium, heavy pot, combine the beans, bay leaf, and enough water to cover by 1 to 2 inches. Bring to a boil. Lower the heat and simmer uncovered, stirring occasionally, until the beans are very tender, 1 1/2 to 2 hours, adding more water as necessary to keep covered. When the beans are soft, mash in the pot with a potato masher or the back of heavy wooden spoon. Remove from the heat.
In a large, heavy skillet, heat the bacon fat over medium-high heat. Add the onions and cook, stirring, until soft, about 3 minutes. Add the garlic, jalapeno, chili powder, cumin, salt, and cayenne, and cook, stirring, until fragrant, 45 seconds to 1 minute. Add the beans and any cooking liquid from the pot, and the oregano, and stir to combine. Cook, stirring with a heavy wooden spoon, until the mixture forms a thick paste, 5 to 10 minutes, adding water 1 tablespoon at a time to keep from getting dry.
Remove from the heat and transfer to a decorative bowl. Sprinkle with the cheese and cilantro, and serve.
Yield: about 2 1/2 cups (4 to 6 servings)