Place a large saucepan over medium-high heat and add in the mushrooms. Season with salt and pepper and cook, stirring occasionally, for 5 to 6 minutes or until the mushrooms have released some of their moisture and are starting to turn golden brown.
Add in the butter, leeks, and garlic, season with nutmeg, salt, and pepper, and cook down for 4 to 5 minutes or until the leeks are tender. Stir in the pasta, water, broth, and wine and increase the heat to high to bring to a boil. Once boiling, reduce the heat to medium to maintain a simmer and cook, stirring frequently, until the noodles are cooked for 1 minute less than the package directions. Stir in the peas and continue to cook until they are cooked and the pasta is al dente. If the liquid simmers too low at any point, just add another splash or water or broth.
Stir through the sour cream, Parmigiano Reggiano, and parsley, and season to taste with more salt and pepper.
