Bring a large pot of salted water to a boil, add fettuccine, and cook until tender with a bite, about 8 minutes. Reserve 1/2 cup pasta water; drain.
Meanwhile, cook prosciutto in a large non-stick skillet over medium-high heat. Cook and stir until prosciutto is crispy, 3 to 5 minutes, and remove from the skillet.
To the same skillet add peas, and cook, stirring, until peas are heated through and lightly cooked, about 3 minutes. Remove from skillet.
Add butter to the same skillet and melt; add cream, stirring, until it comes to a boil, then reduce heat to medium and add garlic and ground nutmeg. When garlic is fragrant, add grated Parmesan. Stir until melted.
Stir cooked prosciutto and peas back into skillet. Taste, season with salt and pepper. If sauce is thicker than desired, add 2 tablespoons pasta water, and stir, adding up to 1/2 cup as needed. Add pasta and toss.
Garnish with fresh parsley, and serve warm.
