Bring a large pot of water to a boil over medium heat. Salt the water, add the pasta and cook to al dente. Heads up: Remove and reserve 1 cup of cooking water just before draining.
Heat the extra-virgin olive oil in a large skillet over medium-high heat. Add the mushrooms and saute until deeply browned and tender, 12 to 15 minutes, adding the garlic, thyme, and sage midway through the cooking. Season the mushrooms with salt and pepper, to taste, and a little freshly grated nutmeg. Deglaze the pan with the Marsala and stir for 30 seconds. Stir in the cream, (or if you prefer, top the pasta with a dollop of ricotta at serving time). Stir in the reserved pasta cooking water, about 1 cup if using ricotta, and just enough to thin out the sauce to your liking if using cream.
Drain the pasta and toss with sauce, parsley, and cheese. Transfer the pasta to a serving bowls and top each with a dollop of ricotta, if using, for mixing into the fettuccine as you eat.