Boil a large pot of salted water. Cook fettuccine until just shy of al dente. Reserve 1 cup of starchy pasta water before draining.

In a large skillet, heat olive oil and 1 tablespoon butter over medium-high heat. Add mushrooms in an even layer. Let sit undisturbed for 3-4 minutes to brown, then stir and cook until moisture evaporates.

Reduce heat to medium. Add remaining 2 tablespoons butter and minced garlic. Sauté for 1 minute until fragrant.

Pour in white wine to deglaze the pan, scraping up any browned bits from the bottom. Let reduce for 2 minutes.

Lower heat to medium-low. Stir in heavy cream, nutmeg, salt, and pepper. Simmer gently for 3-5 minutes until the sauce slightly thickens.

Stir in the grated parmesan cheese until melted and smooth. Transfer the cooked pasta directly into the skillet.

Add 1/4 cup of the reserved pasta water. Toss vigorously for 1-2 minutes until the sauce thickens and coats the noodles completely.

Remove from heat, garnish with fresh chopped parsley, extra parmesan, and serve immediately.