01 - Bring a large pot of salted water to a boil and cook the fettuccine until al dente according to package directions. Reserve 1/2 cup of the pasta water, then drain the pasta.
02 - Heat 2 tablespoons of butter in a large skillet over medium heat. Add the sliced mushrooms and cook for 5 to 7 minutes until golden and tender. Remove mushrooms from the skillet and set aside.
03 - In the same skillet, melt another 2 tablespoons of butter. Add the minced garlic and sauté for 30 seconds until fragrant.
04 - Pour in the heavy cream and whole milk, bringing the mixture to a gentle simmer over low heat while stirring occasionally.
05 - Gradually add the grated Parmesan, stirring until fully melted and the sauce is smooth. Season with salt, black pepper, and an optional pinch of nutmeg.
06 - Return the sautéed mushrooms to the skillet and add the drained fettuccine. Toss everything to coat evenly, adding reserved pasta water as needed to loosen the sauce.
07 - Remove from heat and sprinkle with chopped fresh parsley. Serve immediately with extra Parmesan cheese on the side.