For barbecue sauce: Simmer chicken stock and onions over medium heat for 5 minutes. Add catsup, garlic powder, and brown sugar. Simmer 15-20 minutes, stirring frequently. Set aside.
Rinse chicken in cold water. Drain well. Arrange 25 pieces of chicken on each sheet pan (18 x 26 x 1 inch).
Brush 3/4 to 1 quart of barbecue sauce over chicken in each pan. Bake uncovered until tender, checking frequently. Cook in conventional oven at 425° F for 45 minutes or 375° F in convection oven for 30 minutes. Transfer to steam table pans for serving.Servings: 100