Place chicken in a roasting pan, and season generously inside and out with salt and pepper. Sprinkle inside and out with onion powder. Place 3 tablespoons margarine in the chicken cavity. Arrange dollops of the remaining margarine around the chicken's exterior. Cut the celery into 3 or 4 pieces, and place in the chicken cavity.
Bake uncovered 1 hour and 15 minutes in the preheated oven, to a minimum internal temperature of 180 degrees F (82 degrees C). Remove from heat, and baste with melted margarine and drippings. Cover with aluminum foil, and allow to rest about 30 minutes before serving.
I used the advice that the reviewer on the recipe page said: Use in combination with Moist Garlic Chicken. I sliced 8 garlic cloves and put in cavity, under skin and on top YUM! I also sliced 2 small lemons and put one in cavity and the other on top. Put 1/4 cup butter in cavity and 1/4 cup sliced butter on top. Put cut celery in cavity, and then salt/peppered all over. Roasted for 2 hours - turned out perfect. The GRAVY was AWESOME!! Some flour with the oils, then chicken broth and all the browned bits from the pan and juices from carving. This was my first roast chicken. Will make over and over!!