Bring a large pot of water to a boil, salt it, add the pasta and cook until al dente. Drain, reserving 1/2 cup of the pasta cooking water.
While the pasta is working, in a small saucepan, bring the chicken stock and porcinis to a boil. Simmer until softened, 8 to 10 minutes. Puree in a food processor.
Meanwhile,in a large skillet, heat the EVOO, 3 turns of the pan, over medium-high heat. Add the prosciutto and stir until the fat renders, a couple of minutes. Add the creminis and cook until browned, about 10 minutes. Add the shallot and garlic; season with salt and pepper. Stir in the cream and marsala. Stir in the mushroom puree and cook at a fairly rapid bubble, stirring, until reduced, 10 minutes.
Add the pasta and reserved cooking water to the sauce. Add the cheese as you toss. Serve in shallow bowls; top with parsley.