Start by boiling a large pot of salted water. Once it reaches a rolling boil, add your choice of pasta—fettuccine or linguine. Cook according to package instructions until al dente, about 8-10 minutes. Reserve about half a cup of the pasta cooking water before draining.

While your pasta is cooking, heat the olive oil in a large skillet over medium heat. Add the sliced leeks and sauté for about 5-7 minutes until they begin to soften and turn golden brown.

Once the leeks are caramelized, add the sliced cremini mushrooms and minced garlic to the skillet. Continue to cook for another 5-7 minutes until the mushrooms are nicely browned.

Pour in the dry white cooking broth (or vegetable stock) and let it simmer for a couple of minutes, scraping up any bits stuck to the bottom of the pan. Stir in the heavy cream and allow it to thicken slightly for about 3-4 minutes.

Gradually stir in the shredded Gruyere cheese until it melts into a creamy sauce. If it's too thick, add some reserved pasta water little by little until you reach your desired consistency.

Add your drained pasta directly into the skillet with the cheese sauce. Toss everything together gently until each strand is coated. Season with freshly ground black pepper and salt to taste.

Serve your pasta warm, optionally garnished with chopped fresh parsley.