Brown the sausage; remove from the pan and set aside. In a large skillet, melt the butter or bacon fat over medium high heat and sauté the onion, celery, apples, sage, and salt and pepper. Add the hazelnuts (or pecans), cranberries, and stock and simmer until well heated and the cranberries hydrate a bit. Return the sausage and any juices to the skillet and combine well. Heat through and serve.