Preheat oven to 350°F (175°C) and grease a baking dish.
Melt butter in a skillet over medium heat.
Sauté onion and celery for 5–7 minutes until softened.
Place the seasoned bread cubes in a large mixing bowl.
Pour the butter and vegetable mixture over the bread and toss gently.
Add pepper, poultry seasoning (if using), and salt. Mix lightly.
Gradually add warm chicken broth until bread is moist but not soggy.
Transfer mixture to the prepared baking dish.
Cover with foil and bake for 30 minutes.
Remove foil and bake an additional 10–15 minutes until top is golden and crisp.
Let rest 5 minutes before serving.