In a small heatproof bowl let the porcini and the sun-dried tomatoes soak in 1 cup boiling water for 30 minutes. Remove the porcini and the tomatoes, squeezing them dry, strain and reserve the soaking liquid, and chop the porcini and tomatoes. Mince together the rosemary, the garlic, and 1 tablespoon of the parsley. In a large heavy skillet heat the oil and the butter over moderate heat until the foam subsides and in the fat cook the porcini , the sun-dried tomatoes, the onion, and the rosemary mixture, stirring, for 1 minute. Add the white mushrooms and saute the mixture, stirring, until the mushrooms begin to give off their liquid. Add the reserved soaking liquid, simmer the mixture, stirring occasionally, for 15 minutes, and season the sauce with the pepper and salt. While the sauce is simmering, in a kettle of salted boiling water boil the pasta until it is al dente and drain it. In a heated serving bowl toss the pasta with the sauce and sprinkle it with the remaining 1 tablespoon parsley. Serves 6 as a first course or 4 as an entree. PASTA50