Soak beans overnight. Pour off dirty bean water. Bring beans to a boil and simmer for a shy hour. Meanwhile, in a separate bowl, combine finely chopped onion, garlic, molasses, maple syrup, ground mustard, salt and pepper and let marinate. After an hour of simmering, strain the beanwater and save (you won't need more than 3 c).
Layer raw meat on the bottom of a dutch oven. Rinse beans and cover meat with them. Add 2 c of bean water to the onion marinade then pour the onion marinade over the beans.
Bake for 3 hours at 325 F, but check after 2 1/2 hours and add about 1/2 c of bean water, if needed.
Near the end of the bake, create a glaze by adding the brown sugar to melted butter. And the end of the bake, pour the glaze over the dutch oven's contents. Bake uncovered until no liquid is visible.