Drain beans and reserve soaking liquid. Set aside.
Heat a large sauté pan, lightly coated with oil, over medium-high heat. Caramelize onions, stirring occasionally, until dark brown and very soft. Add peppers and continue cooking for a few minutes until softened. Add garlic and stir to combine.
Transfer vegetables to a slow cooker or Dutch oven. Add beans, mustard powder, paprika, bourbon (or apple cider), ketchup, molasses, salt and pepper. Stir in reserved bean soaking liquid and additional water to equal 4 cups of liquid.
Cook on HIGH in slow cooker for 4 hours until thick and beans are tender. Alternatively, cook beans in a 350°F degree preheated oven, covered for 1 hour. Uncover and continue cooking until thick, saucy and beans are tender.