Preheat the oven to 400 degrees F. Lightly butter a 2- to 3-quart glass or ceramic baking dish.
In a dry saute pan set over medium heat, toast the walnuts until lightly golden brown, about 5 minutes; cool and chop.
Melt the butter in a large skillet over medium-high heat. Add the sausage and cook, breaking up any clumps with a wooden spoon, until brown, about 5 minutes. Reduce the heat to medium and add the celery, onion and 1/2 teaspoon salt and cook, stirring occasionally, until softened, about 8 minutes. Stir in the cranberries and cook to just slightly plump them, about 1 minute, and then remove from the heat.
In a large mixing bowl, add the stuffing mix, sage, thyme and walnuts. Mix together the stock and egg in a large measuring cup, then add it to the mixing bowl along with the sausage-vegetable mixture. Add 1/2 teaspoon each salt and pepper and stir gently to combine thoroughly.
Transfer the stuffing mixture to the baking dish and bake until hot and golden brown on top, 30 to 40 minutes. Serve hot.