Preheat oven to 325. In skillet cook bacon over medium heat until crisp. Remove; drain on paper towels. Crumble, set aside. Drain skillet of all but 1 T of drippings. Cook onion in drippings over medium heat until tender. Transfer to large bowl. Add beans and all but 2 T of bacon; set aside.
In another bowl, whisk together sour cream, broth, flour, rosemary, mustard and pepper. Stir into bean mix. Transfer to 2-qt casserole. Bake, covered, 45 minutes, stirring once halfway through.
In bowl, combine remaining bacon, parsley, and lemon peel; sprinkle on beans just before serving.