Start by rinsing the black beans under cold water to remove any debris. If using dried beans, soak them overnight to ensure even cooking. If using canned beans, drain and rinse.
In a large pot, add the rinsed black beans, 6 cups of water, bay leaf, oregano, cumin, and the whole chili pepper. Bring to a boil, then reduce heat and let simmer for about 45 minutes to an hour, or until beans are tender.
In a separate skillet, heat the oil and butter over medium heat. Add minced garlic and sauté until fragrant, about 2 minutes. Do not let it burn.
Once the beans are tender, add the sautéed garlic mixture to the pot with the beans. Stir in the rice and salt, ensuring everything is well combined. Add additional water if needed.
Bring the pot back to a boil, then reduce to low, cover, and cook for about 20-25 minutes or until the rice is tender and has absorbed the liquid. Remove the bay leaf and chili pepper.
Stir in the tablespoon of vinegar for a touch of acidity. Taste and adjust seasoning if necessary.