1lbdried beans (I used pinto, red kidney, and cranberry beans)
2sheets of kombu ( dried seaweed)
1small onion, sliced
2tspdry mustard (I used Colemans)
fresh ground black pepper to taste
Preheat oven to 350F
Put the beans and the kombu in a large heavy pot. Add enough cold water to cover the beans by at least a couple of inches. Bring up to a boil, then cover, turn off the heat, and put the pot in the oven. Cook the beans for 60-90 minutes, or until they're tender. Test them at the 60 minute mark. I like mine to be tender but not at all soft and mushy.
Remove from the oven and reduce the heat to 200F. Fish out the kombu and discard. Add the all the rest of the ingredients EXCEPT the vinegar and stir well. Cover and return to the oven for another 6-8 hours. Add the vinegar and taste to adjust any seasonings.
The sauce will become thicker if you refrigerate the beans overnight, and they'll keep well for up to a week (probably longer) in the fridge.