Add beans, onion, garlic and spices to slow cooker. For a richer flavor, add option pork fat or bacon to the pot.
Pour the water over the top of the beans and cover. Turn slow cooker on low and cook for 8–10 hours.
Once beans are very tender, remove the pork or bacon if necessary. Remove excess liquid if required.
Use an immersion blender or a potato masher to smash the beans into a relatively smooth texture. Add salt and pepper to taste.