Preheat oven to 300 degrees Fahrenheit. Then, tear bread into 1 inch pieces.
Spread torn bread in a single layer on to 2 sheet pans. Bake bread at 300 degrees Fahrenheit for about 15 minutes, or until bread is crunchy and toasted, without much (if any) darkening.
Place torn and toasted bread in a mixing bowl and set aside.
Dice 1 medium onion and 4 ribs of celery. Dice 4 ounces cremini mushrooms.
Heat 3-4 tablespoons vegan butter on a skillet on medium-high heat.
Place diced onion, diced celery, diced mushroom, and salt in buttered skillet. Saute for 6-7 minutes, or until onions are just translucent. Add 1 clove of minced garlic and your vegan sausage (if you're using it) to your skillet now, and saute for another 30 seconds.
Pour skillet contents on to torn and toasted bread in mixing bowl. Gently stir to combine.
Add finely chopped parsley, dried ground sage, and vegetable broth to your mixing bowl and stir to combine. If you wish to add any other ingredients (toasted pecans or dried cranberries), add them now.
Preheat oven to 350 degrees Fahrenheit. Lightly oil (or vegan butter) a 9 inch by 12 inch baking dish.
Pour uncooked stuffing mixture into oiled baking dish, and gently distribute evenly across dish. Cover dish with aluminum foil, and bake at 350 degrees for 30 minutes. Then, remove foil and bake at 400 degrees for another 10-15 minutes, or until top of stuffing is golden with some crispy edges.