In a large skillet, melt the butter over medium heat. Add the onion and celery. Cook, stirring often, until the onion is golden, about 10 minutes.
Scrape the vegetables and butter into a large bowl. Add the stuffing and parsley. Stir in enough of the stock to moisten the stuffing, about 2 1/2 cups. Season with the poultry seasoning, if desired, and salt and pepper to taste. Use to stuff turkey, or place in a buttered baking dish, drizzle with an additional 1/2 cup stock, cover, and a bake as a side dish.