Preheat oven to 325. Heat a large, deep skillet or pot to medium-high and cook bacon until crisp. Remove bacon from pan to drain on a paper towel-lined plated. Remove all but 2 tablespoons bacon grease from pan.
Add the onions and cook until tender and browned. Add beans, ketchup, brown sugar, dry mustard, Worcestershire, bacon, salt and pepper to the pan. Stir to combine.
Transfer to a baking dish then cover with lid or tin foil and bake 30 minutes. (If using an oven safe dish-leave in and cover) Uncover and bake for an additional 15 minutes.