Melt the butter over medium-low heat in a skillet, add the onions and celery; along with a pinch of salt; cook until tender (about 5 - 7 minutes). Empty the contents of the stuffing mix into a large bowl; add the cooked onions and celery along with the diced apple, cranberries, parsley, sage, and thyme or dried seasonings. Toss well.
In the same skillet add the pork sausage and cook, breaking it up into small pieces. Drain well and add to the bowl. Toss.
Add the chicken stock, a little at a time, stirring until you have the moistness you desire. (Use less for a dryer stuffing, more for a moister stuffing.) Taste, add salt and pepper as needed along with additional seasonings to taste.
Spray, or butter, the bottom of a casserole dish. Spoon the dressing into the dish and then cover with foil. Place in the middle of a preheated 350°F oven. Cook for 30 minutes; uncover and cook for 15 minutes more to get a bit of a crust. Serve.
LindySez: You can make this in advance. Keep covered in the refrigerator. Remove about ½ hour before cooking to allow it to come to room temperature. If not at room temperature, cook covered an additional 15 minutes.