Preheat the oven to 400ºF and grease a 8x8 casserole dish (or equivalent size).
Place bread cubes in a large bowl. Set aside.
Heat butter in a large pan over medium-high heat and warm the butter. Once hot, add the mushrooms and cook until mushrooms are softened and all of the liquid has evaporated.
Add the celery, carrots and onion and garlic and cook until translucent, about 7 minutes. Add the rosemary, sage and thyme and cook until fragrant, about 1 minute. Add the celery mixture to the bread cubes and toss to combine (if adding any optional additions, such as cooked sausage, add them in here). Transfer the mixture to the casserole.
In a medium mixing bowl, whisk together the stock, eggs, coconut aminos and salt and pepper. Pour the eggy stock over the pan of bread cubes. Press down on the cubes with your hands to distribute the liquid evenly.
Cover the casserole pan with foil and bake for 20 minutes. Remove the foil and cook until the stuffing is steaming hot and browned, but not dry, about 20 minutes more.
Serve immediately, or at room temperature.