Brown the sausage if using, drain the fat, remove the sausage from the pan and set aside.
In the same pan, melt the butter and cook the onion and celery until they're wilted.
In a large bowl, combine the crumbled cornbread and the Pepperidge Farm Stuffing. Add the drained sausage if using. Scrape the onions and celery into the bowl with all of the melted butter, plus the salt and pepper. Pour the chicken stock over all of that and combine well. Taste for seasoning and adjust if necessary. Put dressing in greased 9 x 11 casserole dish. The recipe can be made even a few days ahead to this point.
When ready to cook, preheat the oven to 350° and bake for 30 minutes or until the dressing is hot at the center.
Dressing can be made a couple of days ahead and refrigerated unbaked. Be sure to take the refrigerated dressing out at least 30 minutes ahead of baking to allow it to come to room temperature.