*if porcini mushrooms are used cover and soak in hot water for 30 minutes. Cook peas until tender in a large saucepan of boiling salted water, remove with slotted spoon and set aside, reserving cooking liquid.
Fry bacon rinds in a large pot until crisp and fat is extracted. Discard rinds and fry bacon in the fat until crisp. Drain porcinis and filter liquid through cloth or a paper coffee filter to remove grit. Chop finely and add to the pot with the soaking liquid and fresh mushrooms. Stir in garlic and pepper and cook briefly. Toss in parsley and cook for 30 seconds.
Add cream and cook, stirring, until the sauce comes to the boil. Boil until thickened and reduced, 5 to 8 minutes. Begin cooking fettuccine in the water used for the peas. When al dente, drain and transfer to a warm serving dish. Toss with the sauce, and serve with freshly grated Parmesan.