Melt the butter in a skillet over medium heat until it becomes foamy. Add the chopped celery and onion, sautéing them until they become soft and fragrant, which should take about 4 to 5 minutes.

Stir in the minced parsley, poultry seasoning, rubbed sage, and pepper. Continue to cook for another minute to blend the flavors well.

In a large mixing bowl, combine the sautéed vegetable and seasoning mixture with the cubed day-old bread, ensuring the bread is evenly coated with the flavorful mixture.

Pour the beaten egg and chicken broth into the bread mixture. Mix thoroughly until everything is well combined and the bread is moistened but not soggy.

Gently fold the chopped oysters into the bread mixture, distributing them evenly throughout without breaking them up too much.

Transfer the entire mixture into a greased baking dish, spreading it out evenly.

Place the baking dish in a preheated oven at 350°F (175°C) and bake for 30 to 40 minutes, or until the dressing is heated through and the top is golden brown and slightly crisp.