Start by bringing a large pot of salted water to a boil over high heat. Add 12 oz of fettuccine or linguine, stirring occasionally to prevent sticking. Cook the pasta until al dente, about 8-10 minutes. Once done, reserve ½ cup of the pasta water, then drain the pasta and set it aside in a large bowl.

In a large skillet, melt 2 tablespoons of unsalted butter with 2 tablespoons of olive oil over medium heat. Add the sliced leeks and cook them for about 12-15 minutes, stirring occasionally. You'll know they're ready when the leeks turn a golden brown and develop a sweet aroma.

Add 8 oz of sliced mushrooms to the skillet. Sauté the mixture for 6-8 minutes, then stir in 2 cloves of minced garlic and continue to cook for another minute, until fragrant.

Reduce the heat to low and stir in ½ cup of heavy cream and ¾ cup of shredded Gruyere cheese into the mushroom and leek mixture. Keep stirring until the cheese melts completely and the sauce becomes creamy, about 2-3 minutes.

Add the cooked pasta to the skillet, tossing gently to coat it in the luxurious cheese sauce. Gradually incorporate reserved pasta water until you achieve the desired consistency. Fold in the remaining ¾ cup of Gruyere cheese and season with salt and freshly ground black pepper to taste.

Plate your Creamy Mushroom Gruyere Pasta immediately, and for an extra touch, garnish with freshly chopped parsley.