dig a hole that's twice as deep and one foot in diameter larger than the dutch oven you're planning to use.(make sure its big enough to hold all ingredients). next, toss a few rocks or a length of chain into the bottom of the hole.fill the hole with hardwood and then burn the wood down until the hole is three-quarters full of hot coals.
over your open fire (or on a camp stove) precook the beans by slow-boiling them for about 30 to 45 minutes. drain and set aside.
place the salted pork in the dutch oven.layer onions on top, and pour in the beans, molasses, mustard,and black pepper. slice the butter and place on top. add enough boiling water to cover the beans by 1/2 to 1 inch. cover the pot with aluminum foil and then put the lid on and fold foil down sides. make sure the foil is big enough to fold down the sides of your dutch oven this will keep the ashes and dirt out when removing the lid.
shovel out about a third of the coals and put the bean pot in the hole. replace the coals around the sides and on top of the oven; fill the rest of the hole with dirt.cooking time varies, but give it a good 8 hours