Heat the oil in a heavy-bottomed pot or skillet over medium heat. Add the cremini mushrooms and shallots. Sauté until the shallots are translucent and softened, 5–7 minutes.
Add the rehydrated mushrooms, thyme, black pepper, and salt. Sauté for one minute. Add the pasta and the vegetable broth. Bring to a boil, then reduce the heat and simmer, covered, for 10 minutes, stirring occasionally. Uncover the pot and continue simmering until most of the liquid has been absorbed or reduced (DON'T DRAIN!), and additional 2–5 minutes (see Recipe Note #5). Stir frequently, scraping the bottom of the pan with a wooden spoon.
Remove from the heat and mix in the Maggi seasoning sauce, mustard, and sour cream (see Recipe Note #7). Taste for seasoning, adjusting if necessary. Serve immediately, sprinkled with fresh chives or parsley, nutritional yeast (if using), and more freshly ground black pepper.