Drain and rinse the beans.
Heat a pot with vegetable oil and sauté the onion for 5 minutes.
Add cumin, chili powder, and garlic and sauté for another minute.
Add the drained beans, 1 tsp. salt, and two liters of water.
Bring to a boil, then reduce to a simmer. Cover and let it simmer for two hours.
Uncover and simmer until the beans are soft and the liquid has reduced to a sauce-like consistency. Drain, but keep the liquid.
Preheat a large skillet over medium heat.
Add lard or butter, then the drained beans.
Mash the beans with a potato masher or the back of a large spoon while cooking.
Add cooking liquid to achieve the desired consistency over 4-5 minutes, creating a bean purée.