Melt half (3 Tbs) of the butter in a medium/large pan over medium heat - Add the mushrooms and sauté until they have released all their liquid and begin to brown around the edges (apx 6 minutes)
Add the onion along with ¼ tsp of salt and continue to sauté for 3 minutes - Add the celery and continue to sauté for 2 minutes - Add the carrot, garlic, sage, thyme, and pepper to taste - Continue to sauté until onions are transparent and celery/carrots are tender (apx 5 minutes more) - Remove from heat
IF USING, place a medium skillet over medium heat and dry roast your walnuts, almonds, and pecans (or any combination) for 2-3 minutes until they smell very nutty and are slightly darker in color - Transfer to the vegetable mixture
Add the remaining 3 Tbs butter along with the parsley to the vegetable mixture and stir together until the butter fully melts - Adjust seasoning with salt and pepper as needed - Remove from heat
Preheat oven to 350°F
Cut or tear bread into apx ½ inch pieces - Add to the vegetable mixture and stir to coat - While constantly stirring/mixing, slowly add the vegetable stock until fully incorporated - NOTE: It is quite possible that not all of it will absorb into the bread at this point but, not to worry, it will absorb as it bakes - Add the eggs and thoroughly combine
Grease a 9 X 13 inch baking dish or 3 quart casserole - Transfer your stuffing/dressing to the prepared dish and spread into a single layer
Cover with aluminum foil and bake in the top third of the oven for 25 minutes - Remove the foil and bake for an additional 10-20 minutes until the top is golden brown and crispy