In a small bowl, cover the dried mushrooms with 1 cup of hot water and let soak for 1 hour. Remove the mushrooms from the liquid, chop, and set aside. Strain the liquid through a sieve lined with several layers of cheesecloth and reserve.

Prick the skins of the sausages and in a heavy skillet cook them over moderately low heat in the olive oil until they are done, about 30 minutes. Remove to a plate. In the fat in the skillet, cook the onion for 10 minutes, without letting it brown, scraping up the sausage still clinging to the skillet. Add the garlic for the last minute of cooking.

Add the fresh mushrooms, raise heat to moderate, and cook for another 3 minutes.

Add the reserved minced dried mushrooms and their liquid. Over high heat, stirring constantly, reduce the liquid to about 3 tablespoons.

Remove the sausage meat from the skins and crumble the cooked meat into the saucepan, along with the chopped parsley. Add the heavy cream and cook, stirring frequently until the sauce thickens, about 5 minutes.

In a kettle, bring 5 quarts water to a boil and add the salt and vegetable oil. Add the penne, stir, and cook until al dente. Drain and transfer to a serving bowl. Toss with the Parmesan and then the sauce (reheated if necessary). Garnish with the chopped fresh parsley.