Begin by bringing a large pot of salted water to a rolling boil over high heat. Add 12 oz of fettuccine or linguine and cook for 8–10 minutes until al dente. When the pasta is done, reserve ½ cup of the pasta water for later, then drain the pasta and set it aside.

In a large skillet, heat 2 tablespoons of unsalted butter and 2 tablespoons of olive oil over medium heat. Add the sliced leeks and cook for 12–15 minutes until golden brown.

Add 8 oz of sliced mushrooms to the skillet. Cook for 6–8 minutes until softened. Stir in 2 cloves of minced garlic and cook for an additional minute.

Lower the heat to medium-low, pour in ½ cup of heavy cream, and gradually stir in ¾ cup of shredded Gruyere cheese until melted.

Gently add the cooked pasta to the skillet, tossing to coat. If too thick, add reserved pasta water until desired consistency is achieved. Mix in remaining ¾ cup of Gruyere, season with salt and pepper.

Remove from heat and transfer to serving plates. Garnish with chopped parsley if desired. Enjoy hot!