2 pounds ground beef

1/2 cup chopped onion

1 1/2 cups ketchup

1/4 cup white sugar

1/4 cup white vinegar

1/4 cup prepared yellow mustard

1/2 teaspoon celery seed

3/4 teaspoon Worcestershire sauce

1/2 teaspoon ground black pepper

3/4 teaspoon salt

Place the ground beef and onion in a large skillet over medium-high heat. Cook, stirring to crumble, until beef is browned. Drain. Transfer the beef and onion to a slow cooker and stir in the ketchup, sugar, vinegar and mustard. Season with celery seed, Worcestershire sauce, pepper and salt. Cover and simmer on Low setting for a few hours before serving.