Preheat the oven to 300°F.
Lightly butter a 9 x 13 baking dish. Set aside.
While the bread bakes, heat the butter in a separate large saucepan over medium heat.
Add the onion, celery, and carrots. Cook, stirring occasionally, until vegetables are very tender, about 15 minutes.
Pour in the vinegar. Scrape any browned bits to mix with the vinegar.
Bring to a boil. Cook until vinegar is nearly evaporated, about 3-4 minutes.
Add in the sage, thyme, and parsley.
Increase the oven temperature to 350°F.
Add the bread, tempeh sausage, and vegetable mixture into a large bowl. Add 2 cups of the vegetable stock and toss well to combine. The bread should be wet but you won't see any liquid in the bowl.
Add the salt and pepper.
Slowly pour in the rest of the broth, tossing as you add it, until all is combined.
Let rest for 10 minutes to absorb the remaining broth. Adjust seasonings, if desired.
Put the stuffing mix into the prepared dish. Cover with foil.
Bake for 40 minutes. Remove foil.
Increase temperature to 425°F and bake for about 25 minutes more, until golden brown on top.