Cook a pound of beans with a bunch of water - maybe 10 cups or so - on high for 3-4 hours or low for 6-8 hours with a tablespoon or two of salt. Optionally, add a chopped onion, green pepper, a little olive oil, and oja de aguacate (avocado leaves - a couple of those. You can buy them in any Mexican grocery store).
Ladle out some of the water and set aside. Remove the avocado leaves (they're like bay leaves). Mash the beans with a potato masher or process in the food processor. That's it! This makes a lot of beans - you can put them in individual containers and freeze. They're just as easy to pull out of the freezer as the cans are easy to pull out of the pantry!