Bring a large pot of generously salted water to a rolling boil. Add the 1 lb (450g) of fettuccine and cook according to the package instructions until it reaches al dente. Scoop out 1 cup (240ml) of the starchy pasta water and set it aside, then drain the pasta.

Heat a large skillet over medium-high heat and add 1 tbsp (15ml) of olive oil along with 2 tbsp (30g) of butter. Once melted and foaming, add the sliced cremini mushrooms in a single layer. Let them sit undisturbed for 3-4 minutes to develop a golden-brown crust, then toss and cook for another 3 minutes. Remove from the pan and set aside.

Reduce the heat to medium-low and melt the remaining 2 tbsp (30g) of butter in the same skillet. Add the minced garlic and sauté for 60 seconds until fragrant. Slowly pour in the 1.5 cups (360ml) of heavy cream, scraping up any browned bits. Simmer gently for 2-3 minutes until slightly thickened.

Turn the heat to the lowest setting and gradually whisk in the 1.5 cups (150g) of freshly grated parmesan cheese until smooth. Add the cooked fettuccine, sauteed mushrooms, and a splash of reserved pasta water. Toss vigorously with tongs until the sauce is glossy and coats the pasta. Garnish with extra parmesan, cracked black pepper, and fresh parsley.