Rinse and soak beans overnight.
In the morning, rinse beans again and put in the crockpot, on low, for about 6 hours. On the stove, simmer, covered, on medium-low heat for about the same amount of time. Either way, cover the beans with plenty of water and keep adding water as necessary. Keep the beans swimming, you don't want them to get dry!
In a blender or food processor, blend the onion, garlic, pepper, chili powder, and salt until chopped well or pureed.
Put pureed salt mixture into a large frying pan, and put it on medium heat to get it started cooking.
Meanwhile, scoop out beans with a slotted spoon and puree in the blender. You may have to do small batches. Once the beans are pureed, mix in with the heating salt mixture.
Once all the bean puree and salt mixture is mixed together on the stove, let the beans simmer uncovered for about 30 minutes on medium-low heat. Stir every 5 minutes or so.
All done! Store in the fridge for a week.