1 cup unsalted butter, divided
1 large loaf good quality white bread, cut into 1 1/2" cubes
2 cups chicken or vegetable stock
1 tablespoon olive oil
1 pound sweet or hot Italian sausage, casings removed
4 large sweet or yellow onions, chopped
4 stalks celery, thinly sliced
1 tablespoon poultry seasoning
Handful of freshly chopped Italian parsley
Salt and pepper, to taste
Preheat your oven to 350 F. Arrange bread cubes in a single layer on two baking sheets. Bake until bread is slightly toasted and dried out, about 15-20 minutes. Remove from oven and set aside.
Heat oil to medium-hight in a large, heavy skillet on the stove top. Add sausage, making sure to break up into bite-sized pieces with a wooden spoon. Cook sausage until browned and cooked through, about 7-10 minutes. Remove sausage from the pan with a slotted spoon to a paper towel to drain.
Reduce pan to medium heat. Add 1/2 cup butter and onions; toss to coat the onions with the fat. Cook, stirring every few minutes, until the onions are a deep golden brown. The entire process should take about 30 minutes. Season with salt the last few minutes of cooking.
Once onions are cooked, add celery and poultry seasoning to the same pan. Cook until celery is translucent, about 5-7 minutes. Season with salt an pepper. Remove vegetables form heat and let cool for a few minutes.
Add onion mixture, parsley and bread cubes to a large mixing bowl. Add stock about 1/2 cup at a time; toss to combine. Once all stock is used, taste and adjust seasoning. Pour stuffing into a greased 9" x 13" glass baking dish. Press stuffing down gently with your (clean) hands and dot with the remaining 1/2 cup of butter. At this point, you can cover and refrigerate the the stuffing for up to 24 hours before baking.
To bake stuffing, preheat your oven to 375 F. Bake, uncovered, for 45 minutes, until the stuffing is heated through and the top is brown and crispy. Remove from oven and let stand a few minutes before serving.