In a large saucepan over medium-high heat, combine the ketchup, water, vinegar, garlic, sugar, Worcestershire, salt, celery seeds, hot sauce and pepper. Blend and bring to a boil, stirring frequently.
Cover, reduce heat to low and simmer 5 minutes. Add the onions, stirring to blend. Cover and simmer 4 to 6 minutes longer. Serve warm, or cool completely and serve at room temperature.
Recipe by The Tennessee Magazine at https://www.tnmagazine.org/flavor-from-the-underground/