Preheat your oven to 300℉.
Cut bread into ~1 inch cubes, then spread them out on a large baking sheet. Bake for 25 minutes, or until the bread is dry and crunchy like a crouton.
In a large pan or pot on the stove, melt the butter. Once melted, add the diced onion and diced celery. Cook until everything is translucent and soft.
Once the onion and celery mixture is soft, add in the broth, salt and poultry seasoning.
Remove the bread from the oven and space it out into a 9x13 inch baking pan. Turn the oven temperature up to 350℉.
A little at a time (about ¼-½ cup at a time), pour the broth and veggie mixture over the bread and use your hands or a spatula to gently combine it without breaking up the bread. See notes below for suggestions on dry vs. wet stuffing.
Once the stuffing has reached your desired consistency, cover the pan with foil and bake it for 30 minutes.
After the 30 minutes, remove the foil and bake the stuffing for an additional 15 minutes, checking on it to ensure the bread stays golden and does not burn.