Additional freshly grated Parmesan cheese(there can never be too much)
Instructions
Rinse porcini mushrooms. Place in small bowl. Pour 1 cup hot water over and let soak until softened, about 20 minutes.
Drain porcini, reserving soaking liquid. Chop porcini, discarding any hard stems. Set aside.
Melt butter in heavy large skillet over medium heat. Add onion and cook until beginning to soften, stirring occasionally, about 5 minutes. Add sausage, increase heat to high and cook just until no longer pink, breaking up with fork, about 6 minutes. Add fresh mushrooms and dried rosemary and stir until mushrooms begin to soften, about 5 minutes. Add porcini, wine and bay leaf and boil until almost all liquid evaporates, about 4 minutes. Add stock and porcini soaking liquid, discarding any sand at bottom of liquid. Simmer until sauce is syrupy, stirring occasionally, about 15 minutes.
Add pasta to large pot of boiling salted water, stirring to prevent sticking. Cook until just tender but still firm to bite (al dente). Drain. Return pasta to hot pot.
Meanwhile, add half and half to sauce and boil until thickened slightly, about 2 minutes. Add sauce and 1 1/2 cups Parmesan to pasta and stir over low heat until coated. Season with salt and pepper. Transfer to heated platter. Sprinkle with parsley. Garnish with rosemary sprigs. Serve, passing additional Parmesan separately.
Notes
(Sauce can be prepared 2 days ahead. Cool, then cover and refrigerate.)