Preheat oven to 350 degrees F and grease a 9x13 baking dish.
Brown sausage in a skillet, over medium heat. Drain any grease and spoon sausage into a bowl. Set aside for now.
In the same skillet, over medium/high heat, melt butter. Add onions and cook until translucent, about 8 to 10 minutes.
While onions are cooking, mix together stuffing mix, poultry seasoning, salt, pepper, celery seed, sausage, and egg, in a large bowl. Add the butter and onions and stir until well coated.
Now add 3 cups of chicken broth and mix, allowing the bread to absorb the liquid. Add the extra chicken broth if needed. The bread cubes should be soaked, but not dripping liquid.
Pour into the 9x13 dish and bake for 30 to 40 minutes, or until golden brown on top. Enjoy!
