||Preheat oven to 350° F. Season chicken with salt and pepper.
||In medium bowl, combine ketchup, syrup, mustard, vinegar and liquid smoke; mix well.
||Arrange onion slices in bottom of 12 x 9 inch shallow baking pan. Place thighs on top of onions; pour sauce over chicken. Cover with foil; bake 40 minutes.
||Remove foil and bake 20 minutes longer, or until chicken is fully cooked (thermometer inserted in thigh registers 180°F.) and well glazed with sauce.