Sauté onion in bacon drippings in a medium saucepan over low heat until tender. Add catsup, chicken broth, mustard, vinegar, and Worcestershire sauce; stir well. Cook over low heat 15 minutes or until slightly thickened.
Arrange chicken breasts in 13- x 9- x 2-inch baking pans, and pour sauce over chicken. Bake, uncovered, at 350° for 1 hour and 15 minutes or until chicken is tender when pierced with a fork. Baste with barbecue sauce at 15 minute intervals.