Begin by placing potatoes in a Dutch oven, and cover with water, then bring water to a boil. When the water is at a boil, reduce heat to a simmer and cover. Allow to simmer for about 30 minutes or until the potatoes are tender. Then drain the water and allow the potatoes to cool completely.
Next, in a skillet, cook the bacon until crisp. When the bacon is crisp, remove the bacon to paper towels. When the bacon has cooled, crumble or cut into small pieces. Reserve 4 tablespoons of drippings to cook the onions in and discard the rest.
Then, saute the onions in the bacon drippings until tender before mixing in the flour, salt, celery seed, and pepper until combined. Next, slowly add in the sugar, vinegar, and water. Then bring the mixture to a boil over medium-high heat. Continue to cook for 2-3 minutes or until the mixture thickens.
To finish, cut the potatoes into quarter-inch slices and add the potatoes and bacon to the onion mixture in the skillet. Then turn the heat to low and stir gently until the mixture is heated through. To serve, sprinkle with parsley and serve warm!