Baked potato salad

8 slices back bacon
1 cup chopped celery
1 cup chopped Red onion
3 tablespoons flour
2/3 cup cider vinegar
2/3 cup sugar
2 teaspoons salt
1/2 teaspoon ground black pepper
8 cups boiled, peeled and cubed potatoes (about 4 pounds)

In a medium skillet over medium-high heat, fry bacon until crisp. Remove bacon to paper toweling and set aside. Drain all but 1 tablespoon bacon grease from pan. Add celery and onions to bacon grease and saute over medium heat for 1 minute. Stir in flour and mix to form a paste. Slowly add 1-1/3 cups water and vinegar to the skillet and stir until smooth. Continue stirring until mixture thickens and begins to bubble, about 8 to 10 minutes. Stir in sugar, salt and pepper, continue to heat and stir until sugar has dissolved, about 4 minutes. Remove from heat. Crumble reserved bacon and toss with cooked potatoes in a large mixing bowl. Add potato mixture to a lightly greased 3-quart covered casserole dish. Pour vinegar-flour mixture over potatoes, cover and bake in a preheated 350-degree oven until heated through, 35 to 40 minutes.