1. In a large pot, heat 1 tablespoon of the oil over moderate heat. Add the sausages and cook, turning occasionally, until browned and cooked through, about 10 minutes. Remove. When cool enough to handle, cut the sausages into 1/8-inch slices.
2. Heat the remaining 1 tablespoon oil in the pot over moderately low heat. Add the onion and garlic and cook, stirring occasionally, until the onion is translucent, about 5 minutes. Add the mushrooms and cook until golden, 5 to 10 minutes.
3. Add the broth, thyme, red-pepper flakes, 2 tablespoons of the parsley, and the salt to the pot. Bring to a boil. Reduce the heat and simmer, partially covered, for 15 minutes. Stir in the sausages and bring back to a boil. Add the pasta, reduce the heat, and simmer until just done, about 3 minutes. Stir in the remaining 2 tablespoons parsley and the black pepper.
Wine Recommendation: A Valtellina from northern Piedmont will nicely echo the earthy mushroom and spicy sausage flavors here. The wine is made from the nebbiolo grape, as are the more familiar Barolo and Barbaresco.