Preheat oven to 350°F. Place bacon in a large ovenproof saucepan or Dutch oven. Cook over medium, turning occasionally, until fat has rendered and bacon is crisp, 5 to 7 minutes. Transfer bacon to a paper towel-lined plate; discard drippings in pan.

Add onion and 1/2 teaspoon of the salt to pan. Cook over medium-low, stirring occasionally, until golden brown and caramelized, 15 to 20 minutes, adding 1 to 2 tablespoons water at a time, as needed, if onion starts to stick to bottom of pan. Add sweet potato, and increase heat to medium-high; cook, stirring frequently, until sweet potato is softened, 5 minutes. Add tomato sauce, mustard, paprika, and remaining 2 1/2 teaspoons salt; cook over medium-high, stirring frequently, until sauce thickens slightly, about 3 minutes. Add beans, chicken stock, molasses, vinegar, Worcestershire sauce, and butter; stir until combined.

Cover pan, and bake in preheated oven until beans are just starting to bubble around edges, about 35 minutes. Uncover, and bake until caramelized on top and around edges, 25 to 30 minutes. Let stand 10 minutes; transfer to a serving dish, if desired. Crumble bacon, and sprinkle over beans.