Rinse the beans and then soak overnight (at least 8 hours) or boil for 1 hour. Drain and then add to the slow cooker.
In a large skillet, cook bacon, onion, and bell pepper (optional) over medium heat for 6-8 minutes or until bacon fat renders enough to soften the onion.
Stir in the salt, mustard, black pepper, cayenne pepper, tomato sauce, brown sugar, and molasses and then add it all to the slow cooker with the beans. Mix in the broth and then cover and cook on low for 8 hours or until beans are tender. Stir occasionally if possible.
If you want the sauce thicker, let the beans cook on high uncovered for the last 30 minutes