This here is proof positive of why it pays to cook a big pot of beans every week or so and just have them sitting around. With cooked white beans on deck, it took literally twenty minutes to make this soup–which was perfect for last night's exhaustion level.
When making beans that you're planning to use in soup later, you don't need to presoak them. Just pick a time when you'll be home for a couple of hours, throw the beans in with abundant water, bring to a boil, reduce to a simmer and keep on simmerin'. Don't salt the beans until they're starting to turn tender, but DO salt them at some point–they'll be much better seasoned in the end. Use more salt than you think you need to–at least a couple of teaspoons for a big pot of beans.
You can throw in a couple of sprigs of herbs if you like (try rosemary with white beans!), but don't freak out if you don't want to go to the trouble or don't have any herbs on hand.
After about half an hour, start checking regularly–first to figure out when to add the salt, then so you can pull them off the heat when they're just perfectly done. Cool them briefly in the cooking water, then scoop them out with a slotted spoon and divide into 2- or 3-cup portions. You can freeze them, too. I've had good luck with freezing black beans, especially, since you kind of want them to break down in soup. Beans that you want to stay whole and integral during the cooking process don't freeze nearly as well.
You can choose to save the bean cooking liquid for the base of a vegetable soup if you like. But if your family is sensitive to beans (i.e., fart-tastic), go ahead and discard the liquid. It's chock-full of the sugars that are responsible for beans' gassier side effects.
Once the beans are cooked and packaged, you've got tons of flexibility as far as using them. There are quite a few bean soup recipes here already, and many of them are adaptable to whatever sort of beans you've got on hand. Or, if you like, you can open up a jar of sauerkraut and give this quick, very flavorful soup a try. (My kids give it four soup spoons up.)
Sauerkraut and Bean Soup
Adapted from Nourishing Traditions
6 cups strong, flavorful vegetable or chicken broth (you can make a nice homemade veg broth by simmering veg trimmings in the bean cooking liquid for half an hour or so)
2 cups cooked white beans (or 3, if you're not using the sausage)
Optional but highly recommended: 1/2 pound Andouille or other spicy sausage, halved lengthwise and sliced
1/2 tsp red pepper flakes
5 cloves garlic, thinly sliced
2 cups drained sauerkraut, either homemade or Bubbie's (or a similar high-quality brand… NOT CANNED)
Salt and pepper to taste, if you think it needs it (mine didn't–if you're using homemade unsalted broth, you'll definitely need it)
Combine broth, beans, sausage, pepper flakes and garlic in a soup pot. If you're using a homemade, unsalted broth, add 1/2 tsp salt.
Bring to a boil; cover, reduce heat and simmer 15 minutes, or until sausage is cooked through.
Remove from heat and let cool very slightly. Stir in sauerkraut. Taste, season as warranted and serve.