I cook my beans in the Crock-Pot. The night before, sort and rinse beans. Put them in the Crock-Pot and cover with water.
In the morning, drain the soaking water off and cover beans with fresh water. Cook for 3-4 hours on high or 6-8 hours on low (time may depend on your own slow cooker and how hot it gets). I usually cook mine most of the day on high.
After the beans have softened and are done cooking, sauté onion and garlic in oil and butter.
Drain the beans, reserving bean liquid. Add beans to a large mixing bowl. Add sautéed onion and garlic to bowl. Also add the chili powder, cumin, and salt.
Blend beans with electric mixer or by hand with a potato masher, adding reserved bean mixture until beans are the consistency desired.
Serve beans as main dish, in burritos or tostadas, or as a side dish. If desired, top with grated cheddar cheese; heat in oven to melt cheese. Garnish with fresh parsley if desired. We usually make bean burritos with ours (recipe below).