Preheat oven to 350°F. Place the bread cubes in a single layer on a sheet pan and bake for approximately 7 minutes. Set to the side.
In a large sauté pan, brown the sausage with 2 tablespoons of olive oil. While cooking, break apart the sausage into small pieces with a metal spatula or wooden spoon.
Melt a stick plus 2 tablespoons of butter in a large stock pot approximately 4 quarts or more over medium heat. Add the chopped onions, celery, and carrots.
Cook until vegetables are tender-crisp, about 8-10 minutes.
Add 6 cups of chicken broth to the cooked vegetables and bring to a boil. Add the celery salt and pepper. Remove from heat.
Stir in the baked bread cubes and fold in the browned sausage, Pecorino Romano cheese and parsley. Mix together thoroughly. At this point, I recommend sampling and adding salt or pepper to taste, if necessary.
Put oven on broil. Lightly butter the sides and bottom of a large 4-quart casserole dish or aluminum tin (whatever you’re serving in). Transfer the mixed stuffing from the pot to the dish or tin and broil uncovered for approximately 10-15 minutes so the top is crispy and golden brown.