For the stuffing: Heat a large skillet over medium heat and add the butter. When melted, add the celery, apples, bay leaf and onions. Add the poultry seasoning and salt and pepper if using and cook until tender, 12 to 15 minutes. Add the stuffing mix and moisten with the stock. Arrange the stuffing on top of the turkey filling and dot with butter.
Cool and store for a make-ahead meal, or bake to serve immediately. If baking immediately, bake at 375 degrees F until brown, bubbly and crisp on top, 15 to 20 minutes. If baking later, bring to room temperature and bake at 375 degrees F until brown, bubbly and crisp on top, 40 to 45 minutes.