Dry out bread cubes: Preheat the oven to 300 F. Place bread cubes on a large sheet pan and bake for 7-10 minutes, or until the bread has dried out and is slightly crunchy. Remove from the sheet pan and set aside in a large mixing bowl. Increase oven temperature to 350 F.
Saute aromatics: Meanwhile, in a large saute pan, melt the butter over medium heat. Add onion, celery, garlic, parsley, herbs, salt and pepper. Cook for 8-10 minutes, stirring occasionally, until the onion and celery has softened. Transfer mixture to the bread cubes.
Cook sausage: In the same empty saute pan, add spicy Italian sausage and cook over medium heat, breaking up into smaller pieces with a wooden spoon, until browned and cooked through, about 8-10 minutes.
Mix in stock and cranberries: Add 1 cup chicken stock and dried cranberries (if using) to the bowl with bread, vegetables and sausage and mix well. If the mixture looks dry, add up to another cup of stock.
Bake: Pour into a greased 9x13-inch casserole or baking dish. Bake for 30-35 minutes, or until the top is golden brown.