Preheat the oven: Preheat oven to 350°F (175°C). Butter a baking dish and set aside.
Cook the vegetables: Melt butter in a large skillet over medium heat. Add the diced onion and celery and cook until soft and translucent, about 8–10 minutes.
Season: Stir in celery salt, poultry seasoning, salt, and black pepper. Cook for 1 minute to bloom the spices.
Combine: Place the dried bread cubes in a large mixing bowl. Pour the butter and vegetable mixture over the bread.
Add broth: Slowly pour in the chicken broth, gently tossing until the bread is evenly moistened but not soggy.
Bake: Transfer the stuffing to the prepared baking dish. Cover loosely with foil and bake for 30 minutes. Uncover and bake an additional 15 minutes until the top is lightly golden.
Serve: Let rest for 5–10 minutes before serving warm.